REAPER API

From CockosWiki

The REAPER API is family of data types and C++ functions made available to C++ programmers developing plugins for use with REAPER. Some of these functions are also made available via ReaScript for use by ReaPerl and RePython programmers.

The Complete API Function List is here

The ReaScript Function List is here

State chunk definitions are here

The flimsiest beginnings of a Plug-In Architecture description are here.