TextMate is a commercial text editor for Mac OS X. From the TextMate website:
TextMate brings Apple's approach to operating systems into the world of text editors. By bridging UNIX underpinnings and GUI, TextMate cherry-picks the best of both worlds to the benefit of expert scripters and novice users alike.
It features "snippets" (a variation of text completion specifically for code), "bundles" (a package system for themes, syntaxes, etc.), code folding, and other code-specific features.