Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Magnetic - Magnetic is an all-in-one agency management software built for productivity.
7todos - A task board for indie hackers
Zapier - Connect the apps you use everyday to automate your work and be more productive. 1000+ apps and easy integrations - get started in minutes.
TaskPaper - Plain text to-do lists for Mac
Microsoft To-Do - Task management tool