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.
Nifty - Manage projects, work, and communications in one place.
Create Issue Branch - Automates the creation of issue branches on GitHub
ZenHub - ZenHub is how the world's best software teams work together. Trusted by NASA, Docker, and Rackspace. Start free today!
REVISR - Git Management for WordPress : keep track w/ version control
GitScrum - Project management tool for agile teams.