Checklistomania - Centrally managed todo lists for complex processes

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

Pipefy - Pipefy is a process management software that empowers anyone to create and automate efficient workflows on their own without code.

TaskPaper - Plain text to-do lists for Mac

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.

Magnetic - Magnetic is an all-in-one agency management software built for productivity.