Firebase - Firebase is a cloud service designed to power real-time, collaborative applications for mobile and web.
HttpMaster - HttpMaster is a professional software tool for testing and debugging HTTP applications, primarily aimed at REST API applications and web services.
restdb.io - restdb.io lets you create databases and REST APIs quickly. Development databases are free. Powerful web-based and mobile-friendly data management.
Hoppscotch - Open source API development ecosystem
RemoteStorage - An open protocol for per-user storage OWN YOUR DATA
Request inspector - Debug web hooks, http clients