In preparing a project that will require something similar, I’ve found the following (but not evaluated them in depth):
- /Developer/Examples/OpenGL/Cocoa/GLSLEditorSample implements syntax highlighting.
- IDEKit, “an open-source framework that provides programmer source code editing, including syntax coloring, popup functions, and split frames”. This hasn’t been updated for a while (it touts 10.2 and 10.3 compatibility, and comes with a Project Builder project – can be converted with Xcode 2.5).
- UKSyntaxColoredTextDocument.
