My editor ozette is like that (http://www.github.com/marssaxman/ozette/). I wouldn't call it "done", or suggest that anyone else use it, because there are a dozen unresolved bugs and maybe half a dozen unfinished or unimplemented features that seem important - but it's done enough that I spend all day every day using it to make a living. I fix bugs when they annoy me enough to justify the time spent, and I add features when I have time and inclination in my off hours. I suppose I assume that it will be "done" when I've fixed all the known bugs and implemented all the features I had intended before I began working on it, but it seems likely that I could spend my entire career using this tool and still manage to retire before "finishing" it, which suggests that "done" is not a very useful idea here.