PSPSeq is a synthesis and sequencing application for the PSP. Release notes:

i’ve taken the basic synthesis environment i wrote for the ADSP-218x and have ported it to the PSP, adding on a rather ugly but functional interface. the zip file contains versions for firmware revisions 1.0 and 1.5. it should also work for firmware 2.0 but i don’t have access to this revision and have not yet been able to test it out. if you successfully get this to work with revision 2.0, please contact me at pspseq at dspmusic dot org.