NervOS is another shell application for PSP.

Features:

Image Viewer – PNG and JPEG files
Music Player – MP3 files
Can run homebrew – PBP files
Can run ISO/CSO files
Can run UMD’s
Can load prx plugins (some prx plugins may not work)
USB Mode
Shows the current time – hours, minutes and seconds
Shows the battery life percentage
Take screnshots – press Select
Task Manager – press L+R
Multi-tasking
After exiting from a game/homebrew, you are returned to NervOS
Autoboot feature
Shows the volume in a volume bar

http://forums.qj.net/showthread.php?t=137110