Over at the QJ forums, Vermillion has just released Drum Simulator v0.1. As can probably be gathered just by looking at the title, this is a LUA-coded drum simulator for the PSP.

Right now, you can only play one sound at a time (no hitting the high-hats while banging on the snare yet). According to Vermillion, this is due to a delay that he put in between sounds. Without the delay, Vermillion says that the simulator tends to sound like "Joey Jordison on double jump." The coder hopes to sort this out in the next version along with making the sounds better.

For comments and suggestions, click on the 'discuss' link below. Vermillion also says that he'll be doing other instruments that people might want to request, so give him a shout out if you have something in mind. Keep checking back here on QJ for more updates.
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Update: Vermillion updated his app Drum Simulator to v0.2.
Changelog:
-Sounds can be played at the same time!