Undoubtedly my all-time favorite app in Mac OS X. TextMate is just an ingeniously well-thought out programming editor. I myself marvel at how much I love it. The extensibility and simplicity it provides makes it a joy to use. The column select tool is one of my personal favorites.
Migration Score
GOOD
Migration Options
Geany
Geany implements many of TextMates features and even keyboard shortcuts- enough that it was very easy to use.