I can't be bothered to do "proper" documentation, you can just read the source code to work things out.
But I do like reference books - so here are the key functions, organised by type.
Global Objects, Lists and Functions
njin: Core Meta-OS Engine
tite: Tiny Templating
mice: Mouse, Touch and Pointer events
journey: instant navigation using pushState and hashchange
arya: Scrollable areas
blinx: Time and Dates
arty: Canvas, images, SVG
teem: Themes, backgrounds, buttons
vidchat: P2P audio/video calls
mog: Multiiplayer Online Gaming
Math: some extra methods
String: some extra methods
Array: one extra method
JSON: some extra methods