Kostas Familonidis, Software Developer in London, United Kingdom
Kostas Familonidis

Software Developer in London, United Kingdom

Member since November 21, 2013
Kostas is a passionate full-stack developer, most recently focused on cross-platform mobile app development but also experienced with a variety of other projects and platforms, from business process automation to finance and beyond.
Kostas is now available for hire



  • Ruby on Rails (RoR), 10 years
  • Ruby, 10 years
  • JavaScript, 9 years
  • GitLab, 5 years
  • Ubuntu, 5 years
  • React, 4 years
  • D3.js, 3 years
  • React Native, 2 years


London, United Kingdom



Preferred Environment

Linux, Unix

The most amazing...

...thing I've developed is a CRM that integrates mail services in mobile devices.


  • Full-stack Web Developer

    2019 - PRESENT
    Procore Technologies, Inc.
    • Developed the application's stack to support internationalization across all platforms.
    • Reviewed code and supported the team to adhere to the organization's strict QA process.
    • Modernized existing parts of the application's codebase using the latest patterns.
    • Implemented TDD and extensive acceptance-test coverage.
    Technologies: React, Ruby on Rails, JavaScript
  • React Developer

    2016 - 2018
    Vertical Scope, Inc.
    • Developed cross-platform native mobile applications in iOS and Android using JavaScript and React Native.
    • Developed and integrated React components into a forum website using Redux architecture.
    • Improved UX and UI performance on mobile applications.
    • Implemented TDD with Agile development practices.
    Technologies: React, React Native, JavaScript, CSS
  • Full-stack Web Developer

    2017 - 2017
    Pivot.io, Inc.
    • Developed an application for automating business processes in Ruby, Ruby on Rails, JavaScript, and GraphQL.
    • Developed and integrated React.js components using Redux and sagas for concurrent data structures.
    • Transitioned REST APIs and microservices into the GraphQL implementation.
    Technologies: Ruby, Ruby on Rails, React, GraphQL
  • Software Engineer

    2015 - 2015
    SKY UK, Ltd.
    • Developed full-stack applications using microservices in Ruby, Sinatra, and JavaScript.
    • Utilized A/B testing to validate product efficiency on customer retention rates.
    • Maintained and developed multiple custom rack middlewares in Ruby.
    Technologies: Ruby, Sinatra, Rack
  • Lead Developer

    2013 - 2015
    RINGLEY, Ltd.
    • Developed full-stack applications on the intranet/extranet deployed to the cloud.
    • Handled back-end system administration and infrastructure configuration to prepare for distributed computing.
    • Developed a contract management system for tracking job completion and staff performance.
    • Implemented and designed a back-end storage system for optimized performance in MongoDB and MySQL.
    • Implemented and designed an Elasticsearch cloud-based search engine solution.
    • Modernized existing Ruby on Rails applications by extracting business logic, using unit testing, and making use of JavaScript, Ruby, and Ruby on Rails engines.
    • Exposed secure web APIs to integrate with mobile applications.
    • Developed a financial application that monitors and calculates cash flows, payments fees, and percentage fees.
    • Restructured and introduced effective project management methodologies in the organization.
    Technologies: Ruby, Ruby on Rails, JavaScript, CSS
  • Developer

    2013 - 2013
    • Developed a back-end authentication system for a mobile application.
    • Integrated Facebook and Twitter API on the application UI.
    • Developed a full database-driven implementation for multi-language support.
    • Implemented TDD and extensive acceptance-test coverage.
    • Handled the system administration and maintenance of the continuous integration service.
    Technologies: Ruby, Ruby on Rails
  • PMO/Projects Coordinator

    2008 - 2012
    INTRASOFT International
    • Oversaw SLA budgets.
    • Maintained the database backlog for tracking work in progress using Ruby, MySQL, and Linux.
    • Consolidated contracts and delivery of technical documents.
    • Produced and maintained all project documentation, including project plan and project scope.
    • Organized, prepared, and followed up the invoicing procedure, including infrastructure procurement and software license updates.
    Technologies: Red Hat Linux, Bash, Ruby, SQL, HTML, CSS


  • React and React Native (Development)

    Developed and enhanced user experiences on multiple forum sites utilizing React and React Native frameworks.

  • GraphQL Implementation (Development)

    Built a GraphQL implementation from scratch for utilizing very complex data structures and reporting statistics with minimum time delay.


  • Languages

    JavaScript, Ruby, HTML5, Bash, SQL, CSS, GraphQL
  • Frameworks

    React Native, Sinatra, Ruby on Rails (RoR)
  • Libraries/APIs

    Mongoid, React, jQuery, D3.js
  • Tools

    TeamCity, Redmine, GitLab, Git
  • Paradigms

    Object-oriented Programming (OOP), Object-oriented Design (OOD), Functional Programming, Metaprogramming, OLAP
  • Platforms

    Ubuntu, Red Hat Linux, MacOS
  • Storage

    Elasticsearch, Redis, MongoDB, MySQL Daemon, PostgreSQL, Memcached


  • BSc degree in Business Administration (Technology)
    2000 - 2004
    University of Patras - Patras, Greece
  • Red Hat Linux System Administrator
    Red Hat

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