Postman - The Collaboration Platform for API Development
madCodeHook - "madCodeHook" offers everything you need to hook code (mostly APIs).
Insomnia REST - The most intuitive cross-platform REST API Client ð´
Deviare API Hook - Deviare is a professional open source hooking engine for instrumenting arbitrary Win32 functions, COM objects, and functions which symbols are located in program databases (PDBs).
soapUI - SoapUI Pro is one of the most prominent API testing platforms around, allowing developers to quickly prototype the functions of their apps and get them to market with little hassle.
Microsoft Research Detours - Detours is a software package for re-routing Win32 APIs underneath applications.