Capers was proposed as a whole replacement OS for Palm PDA devices a long time ago. There are a series of pages under this one that have applets from Capers available for download if you want to play about with them. They only work on pre-OS5 Palm OS devices, so don’t try them on anything like a Tungsten, you’ll be disappointed. Also they mainly work with MIDI over serial.
In addition to the file downloads, here’s the only documentation I have on these apps. I hope you find it useful.
More Palm related content
If you’re interested in more Palm related posts and pages, here’s some to get you started.