Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Spaces by Google - Small group sharing for everything in life
TaskPaper - Plain text to-do lists for Mac
TickTick - TickTickis a cross-platform to-do list app & task manager helps you to get all things done and make life well organized.
Microsoft To-Do - Task management tool
Haash - Add a smart support community to your website in 3 minutes.