API References
The API programmer references for Rhino and Grasshopper.

RhinoCommon
Rhino.Python RhinoScriptSyntax
Grasshopper (Rhino for Windows)
RhinoScript (Rhino for Windows)
C++ API Docs (Rhino for Windows)
Eto.Forms

compute_rhino3d (python client library for compute.rhino3d)
compute.rhino3d.js (javascript client library for compute.rhino3d)

rhino3dm functionality in .NET
rhino3dm.py (python)
rhino3dm.js (javascript)