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.
Postman - The Collaboration Platform for API Development
Wiplo - The easiest way to organize and run your business workflows.
StopLight - Stoplight is an API Design, Development, and Documentation platform that enables consistency, reusability, and quality in your API lifecycle, all with an easy, enjoyable developer experience.
Toby - Better Than Bookmarks
Mockoon - Mock servers in seconds