Piotr Knapczyk, Developer in Kraków, Poland
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Piotr Knapczyk

Verified Expert  in Engineering

Mobile App Developer

Kraków, Poland
Toptal Member Since
February 13, 2019

Piotr started developing mobile apps in 2011 and has since had the opportunity to work with Microsoft and European Astronaut Centre where he's developed AI technologies with the goal of human exploration of the moon. Piotr has created dozens of mobile apps as both a freelancer and as an independent developer. His main interests are in mobile development and machine learning, however, he also likes to explore different technologies and challenges.


Amazon Web Services (AWS), Push Notifications, Django, Python, KaTeX, LaTeX...
Independent Mobile Developer
NSData, Core Image, Core Graphics, AVFoundation, MapKit, WebView, AppKit, UIKit...
European Astronaut Centre (ESA)
Python, TensorFlow, Keras




Preferred Environment

Kanban, Linux, iOS, MacOS

The most amazing...

...thing I have ever done is work with astronauts on applying AI for lunar exploration.

Work Experience

Freelance Mobile and Python Developer

2019 - PRESENT
  • Refactored an iOS app for healthcare applications. Designed and implemented a new architecture to match business case and back-end services.
  • Performed critical bug fixes on Python (Django) back-end system for healthcare applications.
  • Implemented the Notification Extension for Point Of Sale application allowing for seamless customer experience on the iOS app for iPad with Swift.
  • Implemented a white label app from scratch, serving as a wrapper for a web application. Integrated Facebook login and notification systems (Firebase cloud messaging).
  • Implemented Swift wrapper over KaTeX, a JS Latex library allowing rendering complex latex expressions for use in native iOS apps. Implemented background rendering and cashing to minimise interface interruptions.
  • Seamlessly refactored iOS and Android apps and implemented new features and improvements with no interruptions for 4,000 daily active users.
Technologies: Amazon Web Services (AWS), Push Notifications, Django, Python, KaTeX, LaTeX, Java, Swift, Android, iOS


2011 - PRESENT
Independent Mobile Developer
  • Developed apps for Apple’s App Store, in a variety of technologies, for both iPhones and iPads as well as macOS.
  • Developed Apps downloaded over 600,000 times.
  • Worked on the whole pipeline of building the app, starting from an idea and prototyping, production code, assets, and App Store publishing, marketing, and introduction of new features based on user feedback, finishing on user support and help.
  • Developed applications for a variety of markets and categories including games, productivity apps, reference, image manipulation, and 3D graphics.
Technologies: NSData, Core Image, Core Graphics, AVFoundation, MapKit, WebView, AppKit, UIKit, Kotlin, Android Studio, Objective-C, Swift, Xcode

Machine Learning Trainee

2018 - 2018
European Astronaut Centre (ESA)
  • Researched and developed machine learning architectures for human space exploration.
  • Worked with astronauts on finding the best way to augment their work using machine learning.
  • Developed an entire project from finding requirements, developing data sets, training ML model, and evaluating the results.
  • Worked with multinational, multidisciplinary teams.
  • Prepared data for scientific publications.
  • Used Python to build Keras convolution based models, trained using transfer learning on VCC16 model. Dataset consists of samples gathered by Apollo astronauts on the moon.
Technologies: Python, TensorFlow, Keras

Software Engeener Intern

2017 - 2017
  • Worked on features related to calling for Microsoft Teams.
  • Performed both front-end work as well as using layers for calling.
  • Created prototype features and developed production elements.
  • Worked on projects with millions of active users.
  • Developed code that would be deployed in a multi-platform environment - iOS, web, desktop Mac, and Windows.
  • Worked on accessibility features.
Technologies: Angular, TypeScript, JavaScript

Lead Developer

2016 - 2017
  • Developed an Android application that provides control of the Android device by detecting brainwaves with EEG device.
  • Developed from provided Python prototype into a commercial product.
  • Kept in touch with investor and product lead.
  • Enabled disabled and paralyzed people to communicate with the rest of the world.
  • Developed Android application that can interact with the EEG device and provide an interface for the user.
Technologies: Android, Java

Contract iOS Developer

2014 - 2017
Multiple Companies
  • Developed multiple iOS applications in deferent technologies.
  • Developed features and handled the App Store upload.
Technologies: Objective-C, Swift, iOS

Contract Developer

2015 - 2015
  • Developed the update system for gaming machines.
  • Developed a driver for RS-232 serial port device and implemented Slot Accounting System (SAS) Protocol.
  • Experienced working on drivers for parallel port.
  • Worked on gaming machines for casinos.
Technologies: Qt, C++, Java

Weather on the Way

Swift based app for weather forecast on route. Calculates time of arrival for various points along a route and shows predicted weather forecast the user will encounter. Implemented in Swift, based on Dark Sky API and AppleMaps. Developed the app as from the initial prototype, UI design, functionality finishing on app release and post release management

Weather Radar Widget

A SwiftUI based app that adds weather radar widgets for iOS 14. The app fetches weather radar tiles from an external API and displays them in a Home Screen widget, updating every 10 minutes. Available for iPhones and iPads


Cardbox is the fastest, easiest and most intuitive way to create beautiful visualizations of 3d boxes. Simply drag the design into the left window, adjust sizes of the sides by visually matching them to the template, choose the best perspective for your product and done! The 3d image is ready to be put into a catalog or advertisement.

Available for macOS 10.12 and later


- Drag and drop image in any format including PSD and PDF
- Just one input file - no need to split the design into images for every side
- Dimensions are easily modified based on designs
- Adjust the box in seconds, with live preview
- Snap to align tool for easy manipulation
- Renders in high resolution – up to 50 000 x 50 000 pixels
- Preserve layout while changing designs
- Adjust bevel, material's gloss, and shadow
- Manually enter dimensions directly in inches, cm, mm or pixels
- Supports dark mode in macOS Mojave


The system being developed uses mainly EEG brain waves and EMG signals. EEG waves are cycles of bioelectrical brain activity, while EMG are electrical signals generated by muscles, in this case, the head. These two types of signals are registered using measuring and reference electrodes. The course of these signals is registered continuously, and special software verifies whether they coincide with "pre-loaded" patterns.

These patterns allow paralyzed users to manipulate user interface and communicate with their doctors, family, and the rest of the world.


A community based mobile app. I have refactored and updated both iOS (Objective-C) and Android (Java) mobile apps while working with back-end developers. Added new features, including video playback, Firebase notifications and more.


Calendarium is new, easy to use calendar which gives you a new way to discover many interesting things about this day.

Calendarium combines calendar of historical events with times of sunrise/sunset, number of the week, day, day length, moon phase and more.

–– What our users think ––

" Fascinating!" – Snaarl

"It is a great way to see the history of the day. I always learn something new." - Nancy Rohe

"Use this app every day! Fun to learn new info from a wide time range of history." - M1d2i3v4

"This is a trivia nerd's Nirvana and a history buff's Beulah! Bravo! to the developers of this app!" – jmhillpresley
• #1 App in 3 Countries
• #1 Reference App in 40 Countries
• Over half a million downloads

• On this day in history - Discover historical events and holidays and share it with your friends via mail, Twitter, Facebook or text message
• Sunrise and sunset time
• Planets View - Shows how all planets of the solar system are aligned right now
• Week number, day number, weekday and year
• Number of days passed from 1 Jan and days left until 31 Dec
• Moon phase
• Day length
• Geographic coordinates
• No Internet connection required

Contour Color

Contour Color is the best way to experience coloring for adults. Just download and enjoy carefully crafted designs and beautiful colors.

• Create art and relax in the process.

• Handcrafted color palettes selected by a professional artist

• Intuitive coloring — Color not only by tapping, but just like with pencil on an actual paper.

• Over 100 beautiful and varied designs from many categories from classics like animals and mandalas to zodiac signs, buildings and more.

• Smart color wheel that allows you to choose any color - swipe left and right to change hue, up and down to change saturation and zoom in and out to change the brightness

• Draw within lines or outside as you please

• Eraser and color picker to help you master the craft

• Easily change brush size with a simple slider

• Full Apple Pencil and iPad Pro support.

• No subscriptions — color whenever you want.

• Undo functionality

• Share in high definition with your friends on Facebook, Twitter, or print with an AirPrint printer for FREE.

• New designs coming soon.

Planetary Clock

Planetary Clock is a simple and elegant app what shows positions of all planets of the Solar System at any given day. The app uses a precise calculation to determine accurate positions in real time.

Sun’s and planets sizes are not to scale in order to show them clearly, but other parameters such as the size of orbit, eccentricity, shape of the orbit and position of planets are calculated using precise NASA data.

Planets are also realistically sized to each other.

Just Rain

Relax in the rain with our new app that combines stereo, 3D sound, recorded on location in deferent parts of the world with high-quality video recordings. You will instantly find yourself in a calming place, far away from the noise that surrounds you. Use it to easily fall asleep in the evening or to meditate in the morning. All the benefits of rain without ever getting wet!

Get into the right mood to study, relax, or sleep! Nature’s white noise is there! You will be a sleep machine.

– High-quality 3D recordings, perfect for listening on stereo headphones
– Every recording perfectly matched with high-quality video that will transport you into an audiovisual experience
– Optional timer that stops playback after a specified time. Disable the timer by pressing on the remaining time
– Full offline playback, on both audio and video
– Sound played in the background and when the screen is turned off
– Universal app for both iPhone and iPad, supporting all new devices such as iPhone X and iPad Pro
– New rain acenes coming soon
– 82 minutes of audio recordings

Krak Tram Map

App that shows the current location of all trams in Cracow, Poland. The map is updated every 10 seconds.

Catch The Sun

Watch out for nasty spiked blobs and try to collect as many points as you can before the screen is filled with enemies!

Catch The Sun is a simple, colorful, and fun arcade game that forces you to make fast decisions and practice your reflex!
Collect power-ups to slow down enemies and act fast to receive bonus points.

Are you ready for a challenge?

Thick Red Line

Thick Red Line - drawing thick lines with constant on-screen width for SceneKit with metal shaders.
2019 - 2020

Master's Degree in Computer Science

AGH University of Science and Technology - Kraków, Poland

2014 - 2018

Bachelor of Engineering Degree in Computer Science

AGH University of Science and Technology - Kraków, Poland


Course in Space Rendezvous and Docking

European Astronaut Centre, European Space Agency


Keras, PyTorch, Core Graphics, Core Image, KaTeX, Apple Maps API, Game Center, WebRTC, Node.js, SciPy, TensorFlow, OpenGL, OpenGL ES, Android OpenGL, Facebook Login


Xcode, iTunes Connect, Git, Shell, Photoshop 7, Illustrator CC, Blender, Apple Push Notifications, Fastlane, Android Studio, WebView, GIS, Apache Maven, Final Cut Pro X, Jira, Confluence, Firebase Cloud Messaging (FCM), LaTeX


iOS SDK, UIKit, Swagger, Android SDK, Unity, AppKit, ARKit, MapKit, Django, SwiftUI, Angular, Qt, Ruby on Rails (RoR), Flask


Mobile Development, Promise, Unit Testing, Object-oriented Design (OOD), Kanban, Model View Controller (MVC), REST, Scrum, UI Design, Dependency Injection


Swift, Objective-C, Python, Swift 5, Kotlin, C++, Java, Scala, Ruby, JavaScript, TypeScript, SQL, XML


iOS, MacOS, Mobile, Linux, Firebase, Apple TV, Amazon Web Services (AWS), Android, Web, Arduino, Windows, Ubuntu


JSON, Amazon S3 (AWS S3), MySQL, NoSQL, PostgreSQL, SQLite


App Store, iPad, iPhone, iOS Camera, Computer Vision, Computer Vision Algorithms, HTTP Live Streaming (HLS), Machine Learning, ML Kit, UI Testing, AVFoundation, Deep Learning, Swift Optionals, APIs, Machine Vision, Augmented Reality (AR), NSData, Software Development, Image Processing, Data Visualization, Algorithms, Push Notifications, Widgets, Computer Science, Web Development, Design, 3D Design, Early-stage Startups, Startups, Startup Consulting, Firebase Hosting, Games

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