Graphite2 is a rework of the original Graphite engine that is faster, smaller, and uses an API that is better suited to the layout architecture of most text-processing applications.
The Graphite compiler is a tool that is used to compile together a TrueType font and GDL program describing font behaviors into a Graphite-enabled font.
The package includes the program and various documentation files, such as a description of the Graphite font tables, debugger file documentation, a formal GDL grammar, etc.
Go to Graphite font download page.
GDL documentation - the main GDL reference paper:
Sharon Correll, 2012-01-13
Download "GDLdocumentation.pdf", Acrobat PDF document, 266KB [3698 downloads]
GDL tutorial - an introduction to GDL programming:
Sharon Correll, 2012-01-05
Download "GdlTutorial.zip", ZIP archive, 490KB [1057 downloads]
Also see the online tutorial.