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.

Public - Group chats.

Todoist - Todoist is a to-do list that helps you get organized, at work and in life.

Spray - Local chat, made simple

Sendtask - Sendtask is the easiest way to organize your work and collaborate online. Simple to use but powerful enough to run your business on it.

Chalk - Chalk is a calculator that tries to do right what others do wrong.