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.
Streaks - The to-do list that helps you form good habits.
Create Issue Branch - Automates the creation of issue branches on GitHub
Taskful - Deadlines, meet your match.
REVISR - Git Management for WordPress : keep track w/ version control
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.