GitKraken - The intuitive, fast, and beautiful cross-platform Git client.
BookWidgets - BookWidgets is an excellent application that let you create engaging exercises in minutes and easily share a varied variety of beautiful and fun activities with your classroom and others.
SmartGit - SmartGit is a front-end for the distributed version control system Git and runs on Windows, Mac OS...
Padlet - Visual boards for organizing anything.
SourceTree - Mac and Windows client for Mercurial and Git.
Quizlet - Quizlet allows you to review and create flashcards for a variety of subjects, such as math and reading.