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.
Chars - Unicode Symbols Keyboard for iOS
GoodGantt - The best Gantt chart for Trello®
Falcon for iOS - Writing notes made simple
Paws for Trello - The best way to use Trello on your desktop
A5 - Takes notes in your browser. Elegant & simple.