ReqRes - A hosted REST-API ready to respond to your AJAX requests.
Asana - Asana project management is an effort to re-imagine how we work together, through modern productivity software. Fast and versatile, Asana helps individuals and groups get more done.
JSON Placeholder - JSON Placeholder is a modern platform that provides you online REST API, which you can instantly use whenever you need any fake data.
Teamgantt - Intuitive project planning and collaboration. Beautiful Gantt charts, task-level communication, file sharing, resource management and more.
JsonAPI - Application and Data, Languages & Frameworks, and Query Languages
Basecamp - A simple and elegant project management system.