Flow
Luke

A formspec library that automatically positions and sizes elements

Formspec AST
Luke

A library to help other mods interpret formspecs.

HUD FS
Luke

A library to make HUDs from formspecs

flinv
Luke

API to add new inventory tabs which work across different inventory mods

FS51
Luke

Compatibility layer for formspecs

Squill
Luke

A subset of SQL. No complex installation required.

SSCSM implementation
Luke

A server-sent CSM library.