TextMate is a general-purpose GUI text editor for Mac OS X created by Allan Odgaard. Notable features include declarative customizations, tabs for open documents, recordable macros, folding sections and snippets, shell integration, and an extensible bundle system.
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TextMate has an extensive library of plugins which can be further extended to make it even more powerful.
Pro Open source
Textmate is open source and hosted on GitHub.
Pro Lightweight footprint
It's lightweight footprint makes it extremely fast to load and use.
Pro Multi line select and editing
Pro OS X only (native)
Con OS X only
TextMate is for OSX only.