psps with firmware 1.0 (not 1.5, so that means only jap models that have not been updated) have now lots of homebrew running on them e.g, a Gameboy emu, and homebrew games and apps
http://psp-news.dcemu.co.uk/gameboyemupsp.shtml
http://psp-news.dcemu.co.uk/portabletetris.shtml
http://psp-news.dcemu.co.uk/textviewer.shtml
http://psp-news.dcemu.co.uk/marioworld.shtml
here for the rest
http://psp-news.dcemu.co.uk/
that was quick!