I suppose TextMate was a bit more niche, being OS X only, but at one point it seemed to be everywhere.
Hmm, while we're counting, what about BRIEF? At one point, widely enough used that Visual Studio even had BRIEF emulation!
(When I was starting out in software development, almost all of my colleagues used this. Now just a footnote.)
BRIEF by UnderWare! I loved that editor. I particularly liked the “go to this line number, but use the line number before unsaved edits”. This let you compile a file, get the error log, then start making edits; but the line numbers in the error log were still useful.