Don't forget about the built-in help! Press F1 anywhere in the editor to get help about the current screen.
A quick reference of all the keyboard controls in CUSTOM.
A quick reference to the controls used when playing games.
A contents page for plotscripting articles on this wiki.
An introductory step-by-step guide to writing plotscripts.
The plotscripting dictionary is a complete listing and documentation of available plotscripting commands. A scan through is recommended to confident new plotscripters to get an idea of what their scripts could do.
The dictionary is also packaged with engine downloads. The link above is the documentation for the latest stable release (please ignore the incorrect remark at the top that it documents nightly builds).
The version of the dictionary for current WIP (nightly) builds is here.
Definition of the language in which plotscripts are written, HamsterSpeak. Not aimed at non-programmers.
How to get the source, how to compile it, and source documentation (including plans).
A list of known bugs and their states.
Pretty good documentation of the internals of RPG files, for OHR developers.