Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
GitKraken - The intuitive, fast, and beautiful cross-platform Git client.
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
SourceTree - Mac and Windows client for Mercurial and Git.
Slack - A messaging app for teams who see through the Earth!
GitHub Desktop - GitHub Desktop is a seamless way to contribute to projects on GitHub and GitHub Enterprise.