Duolingo - Duolingo is a free language learning app for iOS, Windows and Android devices. The app makes learning a new language fun by breaking learning into small lessons where you can earn points and move up through the levels. Read more about Duolingo.
Jenkins - Jenkins is an open-source continuous integration server with 300+ plugins to support all kinds of software development
SmartCards+ - Spaced Repetition Software for iOS. Modern, powerful and easy to use.
CircleCI - CircleCI gives web developers powerful Continuous Integration and Deployment with easy setup and maintenance.
Zorbi - Spaced-Repetition Flashcards - Other tools are built by boomers, Zorbi is built by students.
Travis CI - Focus on writing code. Let Travis CI take care of running your tests and deploying your apps.