A Krita clone
It's that it's been around since 1997, and can do a lot more than we, but take a look at
http://pixel32.box.skIt's even got a performance tests menu item :-). I'm impressed by the application, not just by its price tag, but also by the fact that the author has made a more-or-less complete photoshop clone _and_ has written his own cross-platform widget set for it.
In other news: Michael Thaler has improved the performance of our scaling routines by more than 100% while still retaining the excellent quality. We can now not only scale with the best, but also with the quickest!