Brunni has released OldScholl Library for PSP. Oldschool library is a library designed for creating 2D games, apps or demos for your PSP. It's brings you all the power of the PSP graphic processor without having to learn lots of 3D and internal hardware concepts. It's very easy to use and flexible.

For example, you can load PNG images with alpha channel, deform them (zoom, rotation, transparency, tinting, bilinear filtering, ...), directly draw on them, draw maps, 4-point gradients, debug message boxes & console and so on.
You can also play audio files (.wav & .bgm), stream them from Memory Stick. It includes a key handler, so you can get when a key was pressed or is currently held, set autorepeat values for some pressed keys.