Yoshihiro has ported a Nintendo DS emulator to the Sony PSP.
It's still too slow to be playable and won't run all games but it's better than the previous attempts.
The DSONPSP emulator is based on DeSmuME v9 core, and has a file browser, frame skip, vertical and horizontal display options and a few other settings.
For those interested both the download and a screenshot are available below.
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