Postman - The Collaboration Platform for API Development
madCodeHook - "madCodeHook" offers everything you need to hook code (mostly APIs).
Apiary - Collaborative design, instant API mock, generated documentation, integrated code samples, debugging and automated testing
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).
Django REST framework - Django REST framework is a toolkit for building web APIs.
Microsoft Research Detours - Detours is a software package for re-routing Win32 APIs underneath applications.