Gabriel Gircenko, Developer in Zagreb, Croatia
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Gabriel Gircenko

Verified Expert  in Engineering

Android Software Developer

Zagreb, Croatia
Toptal Member Since
November 10, 2016

For the past nine years, Gabriel has worked as a developer specializing in Android software. He has worked on multimillion-dollar user apps. He is passionate about proper development processes and knows how to foster them. Lately, he has immersed himself in leading teams with a proper Scrum framework. Gabriel communicates exceptionally well and has been on teams of all sizes.


Scrum, Google Play Store, Android Studio, Android SDK, Git, Gradle, Firebase...
Minds + Assembly
Scrum, Android Studio, Android SDK, User Experience (UX), Git, Gradle, ARCore...
Android Studio, Android SDK, OWASP, Java, Android




Preferred Environment

Scrum, Jira, Model View ViewModel (MVVM), Git, Kotlin, Android Studio, Slack, Android Jetpack, Jetpack Compose, Scrum Master

The most amazing...

...contract is the one where I gradually progressed from the tech lead architect to project manager to product owner—from 1 project to 3, from 5 people to 14.

Work Experience

Owner | Android Consultant

2014 - PRESENT
  • Founded a company to get more reliable job opportunities.
  • Built three apps from scratch and managed them until deployment.
  • Managed, led, and taught two developers successfully.
  • Learned about business in general how to build and grow one.
  • Helped clients reach their goals and deadlines every time.
Technologies: Scrum, Google Play Store, Android Studio, Android SDK, Git, Gradle, Firebase, REST, Java, Android, Slack, Kotlin, User Experience (UX), Maps, Google Maps SDK, SDKs, Augmented Reality (AR)

Senior Android Engineer

2019 - 2019
Minds + Assembly
  • Acted as Android lead engineer with Minds + Assembly in a five-person team.
  • Replaced the previous developer and co-captained the completion of the Android app on a tight deadline schedule.
  • Developed my first commercial app with Kotlin and ARCore library.
  • Built custom controllers, which utilized only a drag gesture to successfully interact with an object in 3D space.
  • Animated multiple VR/AR objects moving on a click.
  • Increased the knowledge of the technology tremendously over the course of the project.
Technologies: Scrum, Android Studio, Android SDK, User Experience (UX), Git, Gradle, ARCore, Kotlin, Android, APIs, Augmented Reality (AR)

Senior Android Engineer

2019 - 2019
  • Documented all the details extensively in a simple 15 page Google Docs file, which made the client extremely happy.
  • Wrote a few suggestions based on OWASP Android security guidelines.
  • Suggested Kotlin language to replace old Java language.
  • Chose technologies for the client, such as Chrome over WebView, because the Chrome web browser is safer from hackers.
  • Overcame a clunkily built UI, which had no usage of dimensions, styles, and unnecessary text sizes, by fixing UI bugs and making design suggestions; the client was delighted with the document.
Technologies: Android Studio, Android SDK, OWASP, Java, Android

Senior Android Engineer

2016 - 2018
  • Developed two apps from scratch and worked on them as the only Android developer.
  • Implemented beta testing with HockeyApp crash reporting.
  • Used a 3D library called LibGDX for demonstrating and interacting with 3D models.
  • Implemented fresh changes for three complex screens without damaging any previous functionality.
  • Used Retrofit for all the REST requests and a Picasso library for image handling.
  • Implemented a chat and in-app, real-time notifications with Firebase.
Technologies: Scrum, Google Play Store, Model View Presenter (MVP), Push Notifications, Android Studio, Android SDK, User Experience (UX), Java, Firebase, LibGDX, HockeyApp, Git, REST, Google Maps, Android, Slack, Gradle, APIs, Maps, Google Maps SDK, SDKs, Augmented Reality (AR), OpenGL, Android OpenGL

Senior Android Engineer

2015 - 2016
  • Developed two premium video-content-streaming apps with millions of users and their library.
  • Made improvement suggestions, 90% of which were adopted.
  • Learned about VIPER, architecture variation in MVP, and worked in TDD with Mockito and PowerMockito tests.
  • Worked on a variety of tasks, as needed, including caching, fixing bugs, making improvements (UI, memory, code), sending tracking data, writing tests, changing models according to JSON responses, and more.
  • Collaborated with five people daily in a team of over 20 people.
Technologies: Scrum, Unit Testing, Model View ViewModel (MVVM), Jira, Android Studio, Android SDK, Java, Git, Mockito, Android, Gradle, APIs, Over-the-top Content (OTT), SDKs

Yahoo Daily Fantasy
Yahoo Fantasy Sports is a fantasy sports app delivered in three months. I was in charge of updating features in the Daily Fantasy part of the app while also updating the code from Java to Kotlin and various architectural patterns to MVVM with RxJava. Also, I built guides for the refactoring for other developers to follow.
• Built my tasks according to product directions.
• Used Agile and Kanban with daily scrum meetings.
• Helped update different developer guides and Jira ticket templates and helped optimize processes inside the team.


I developed two premium content-streaming Android applications and their libraries, and my most significant contribution was making the UI code more robust. Until then, there had been more than two bug fixes per week on the UI. After that, we changed the UI only if the specifications changed.

Technologies: Android, TDD, Java, Mockito, PowerMockito

Kotlin vs. Java: All-purpose Uses and Android Apps | Blog Post

Kotlin and Java are two powerful general-purpose languages popular for Android and beyond. I wrote a blog post where I discussed their top features and differences, then focused on how to smoothly transition between the two.

Safe in Home | Wear OS: Toptal Project
I participated in the five-people team that Toptal Projects provided for the client, including one senior and junior delivery manager, project manager, and UX/UI designer. I communicated daily with two product owners, one DevOps, and two technical support persons, leading another Android senior engineer.

• I acted as a go-to tech person for this project, performing as an Android architect/lead engineer.
• Took responsibility for research and development and took critical project risks. Researched the market and watched by requirements of the client.
• Set up epics and stories for the MVP in collaboration with the team
• Built a roadmap for delivery.
• Wrote the setup guide for the app to work correctly in the Kiosk mode on the smartwatch.
• Built native calls functionality with custom UI (not VoIP).
• Helped hire a great addition to our Toptal Projects team—a senior Android engineer—who complemented my skills perfectly.

Onfido | Identity Verification SDK
I was in charge of implementing a screen reader accessibility feature from scratch. Working there was one of my best work experiences.

Successfully finished adding the accessibility feature to every screen.

Player FM
Most of my work on this project consisted of updating the UI and implementing Android Wear API for an urgent release of the podcast application. This was my first Kanban project, made in Android Studio, and hosted on GitHub.

Technologies: Android, Android Wear

Automation Tool for Job Seekers
A tool for automating the job application process.

I hired two sales representatives through an online freelance agency to help me apply for different positions and gradually automate the process.

We had meetings every day to go through the updates. I introduced advanced and complex usage of Google Sheets' pivoting, formulas, and charts to track rewards for the sales representatives and their performance within two different sales approaches. I also wrote extensive documentation to help us stay on the right track.

With Zapier, I automated generating leads and notifications for assignees in Slack after updates to statuses. I had two mentors and meetings once a week with each.

Plume Workpass
I worked with Plume on an enterprise app called Plume Workpass. I was part of an Android team of 10 and more than 100 people working on this app.

This was my first project with a clean architecture and a Kotlin multiplatform. I contributed to almost every part of the app—from the data layer through the domain and presentation to the UI. One very useful concept I learned was the mappers between each layer in the clean architecture.

Jumprope | How-to Videos

I was in charge of bug fixing and implementing new features.
It was a one-month engagement, but in that time, I fixed all the bugs that came my way and helped finish one beta feature.

Jumprope was acquired by Linkedin in 2021.

This app is a personalized weight-loss program and I worked as a lead Android engineer in a team of five for two months.

The biggest challenge was to make changes in a legacy code and an architecture that didn't follow MVP principles as intended.

The Top App for Mothers

I worked on this mother-targeted app that ranked number one for downloads in its country. I co-developed the Android version from scratch and was mainly in charge of the UI. Delivering the required customization made this a fun project.

Technologies: Android, Analytics

TAKH Tutor AR is an AR/VR app that educates patients about their healthcare products.

I was the lead Android engineer using Minds and Assembly in a five-person team. I also worked closely with an in-house iOS developer and a 3D designer to match the experience. Another Android developer and I were in charge of finishing the Android app within tight deadlines.

Project Highlights:
• Developed my first commercial app with Kotlin and ARCore library.
• Built custom controllers that utilize only a drag gesture to successfully interact with an object in 3D space.
• Animated multiple VR/AR objects that moved with a click. I increased my knowledge of the technology tremendously throughout the project to make this possible.

Vimvest | Organized Investment Goals
Developed alongside two senior Android engineers. I was in charge of bug-fixing and implementing new features.

Although I was hired for short-term help, I learned a lot about Android Jetpack, Dagger 2, and Coroutines.

FYX Driver
I worked as the sole senior Android engineer building an MVP of the app from scratch to publish, and I was in charge of publishing updates. This was one of two enterprise apps I developed for FocustApps.

Technologies: Android, Google Maps, REST, Git, HockeyApp, libGDX (3D), Firebase, Google Cloud Messaging

FYX Mechanic
I was the sole senior Android engineer building the MVP of this app from scratch and publishing it along with updates. This was one of the two enterprise apps I developed for FocustApps.

Technologies: Android, Google Maps, REST, Git, HockeyApp, libGDX (3D), Firebase, Google Cloud Messaging

Crorex | HFT EA | Project Manger

This was a fintech company with aspirations to become a private hedge fund.
I managed a team of four highly driven people, including one trader, one sales representative, one quant algorithm engineer, and an engineer in charge of automatizing processes.
• We developed an EA (expert advisor) with a hedging algorithm in MQL4. 90% of direction guesses are successfully closed in profit.
• I was in charge of organizing meetings, standups, work sessions, PR reviews, occasional EA feature development, accounting, and much more.
• Kanban organized in Trello with daily scrum standups.
• This was a side project for all of us.
• The biggest challenge was to get everyone on the same page and charge for the same goals.


A scientific research app for a skin disease called HVS.
I made the app from scratch with a Clean version of MVVM (Model View ViewModel) architecture.
Although I did regularly publish the app to Beta testers via Firebase Releases, I didn't stay on board to publish it live

Idyllic | Identity App and Code Review

Idyllic was in a pre-investment stage, and they needed a well-documented code review. In one week, I wrote more than 20 pages in a Google Doc file with a heavy emphasis on security. In addition to the in-depth security review, I also gave code improvement suggestions, composed bug reports, and showed design improvement according to Android design guidelines.

Droidcon Zagreb 2015 | Publication

I delivered a speech titled "From Android Beginner to a 5-star Freelancer." This was my first professional talk, and I enjoyed speaking and sharing my knowledge about freelance work. After the speech, I obtained one business deal and a few developers approached me for a job, which was great.

The link attached is an article written about the talk (in Croatian).


I co-founded the TaxiCentral startup. Our goal was to make a super easy-to-use app for people who want to order a taxi in Zagreb. Basically, it was like Uber for taxi companies.

I was responsible for the entire development, rollout, and everything in between—working on the architecture, documentation, partial design, testing, publishing, and promotion. This was my first published application.

Technologies: Android

LandKeeper | Hackathon
I developed the Android part while my college peers implemented the web crawling for this project. We won first place and received other perks like free office space for a year. The link attached is our pitch for the project (in Croatian).

BookBottles | Project Manager
BookBottles helps nightclubs easily manage reservations, table inventory, guest lists, client profiles, and transactions. I implemented the communication between the client and our developer on this project.

Dir po Zagrebu

I built an Android app from scratch with a Parse-based back end for a pub-crawling brand for this project. I also set up everything so the founders could easily add events to the Parse back end.

Technologies: Android, Parse


The client's goal was to publish an Android pub-crawling app to the Google Play Store. They chose me to develop it after I reviewed the two previous developers' code.

I implemented the full development of the Android and Parse back end, completing the weekly tasks I had brainstormed with the client. I also migrated the app from Eclipse to Android Studio and the back end from DreamFactory to Parse.

Technologies: Android, DreamFactory, Parse, Facebook integration

Conference App for Dubai

The client's goal was to complete a partially (70%) completed app. They had previously employed four freelance developers who each, in turn, did some work before moving on. The code was in terrible condition and the client had a very tight schedule.

I worked on the UI changes, database, and REST API without improving the code because of the tight schedule and limited budget. The client delivered a fully developed app on time.

Technologies: Android, SQLite

AP Jets | Luxury Air Charter
I was in charge of building a POC (proof of concept) app in Flutter. This was my first professional project in Flutter, and I was amazed at how fast you can develop features and easily connect with the back end. Unfortunately, before I could finish the app, the budget for the project ran out.

Priority Keeper | Flutter Side Project
Occasionally working on this app helps keep my priorities straight.
I'm learning Flutter and Firestore with it. A simple app that can have multiple projects and tasks inside each. You see only the highest priority tasks from each project on the home screen.
2022 - 2022

Goal Setting At Work: Plan for Success and Reach Your Goals in Mentorship

Udemy - Online


Professional Scrum Master I


Goal Setting at Work: Plan for Success and Reach Your Goals



Google Maps, Google Geocoding API, Google Maps SDK, Retrofit, Google Maps API, Facebook API, Selenium WebDriver, Google Play API, RxJava 2, OpenGL, Android OpenGL


Android Jetpack, Trello, Android Studio, Git, Gradle, GitLab, Jira, GitHub, Slack, Google Docs, Google Sheets, Flow, Crashlytics, Asana, Figma, Zapier, Docker Compose, Fastlane, Android NDK, Firebase Analytics, Looker


Android SDK, Flutter, LibGDX, JUnit, Mockito, Dagger 2, Selenium, Espresso, KOIN, Alembic


Java, Kotlin, Clean, XML, Python 3, Python, Dart, GraphQL, MQL4, C++, Swift


Model View Presenter (MVP), REST, Kanban, Model View ViewModel (MVVM), Scrum, Unit Testing, Agile, Clean Architecture, Dependency Injection, Waterfall Development, Management, Model View Controller (MVC), Clean Code


HockeyApp, Android, Mobile, Firebase, ARCore, Google Cloud Platform (GCP), Docker, Amazon Web Services (AWS), iOS, AWS Lambda


SQLite, Amazon S3 (AWS S3), Cloud Firestore


User Experience (UX), User Interface (UI), Mobile GPS, Lifecycle-aware Components, Coroutines, Sprints, Room, Android Wear, Android Wearables, Wearable Technology, Wearables, SureMDM, Scrum Master, Android Wear OS 3, Data Binding, Android Data Binding, Google Drive, Google Calendar, Hilt, Jetpack Compose, Android Architecture, Wear OS, Leadership, Planning, PSM-1, Minimum Viable Product (MVP), Localization, Over-the-top Content (OTT), Maps, SDKs, Generative Pre-trained Transformers (GPT), Open Source, Augmented Reality (AR), Bluetooth, Push Notifications, Agile Sprints, Google Material Design, Google Play Store, OWASP, Jira Administration, Jira Administrator, Goal Management, Mentorship, Team Mentoring, Mentorship & Coaching, Kotlin Multiplatform, Selenium IDE, Screwdriver, Enterprise SaaS, APIs, FastAPI, Large Language Models (LLMs), OpenAI GPT-4 API

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