Acme is the part that I use even under OS X. The regexes are cool (they are recursive), it is easy to process a selection through a shell command, and the compi

Acme is the part that I use even under OS X. The regexes are cool (they are recursive), it is easy to process a selection through a shell command, and the compiler integration is both simple but really useful. I think what I like so much is that it is a rare example of an expert ui, designed for when you are really proficient rather than for learning or discoverability.