Whimsical Sticky Notes - Visual project management using sticky notes
HeySpace - HeySpace is the only free task and simple project management software with communication and collaboration feature.
Jot - The no-fuss way to take notes
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.
Gone - An ephemeral to-do list
Taskade - Make lists, organize your thoughts, and be inspired to get things done. Taskade is a collaborative space for your tasks.