I'm not very knowledgeable in this world, I don't even know if the gadget API is standard or not.
More specific requirments:
- Runs on Unix (preference for Debian)
- Free software (free as in free speech, not free as in free beer)
In free software, a friend suggests me dropthings which seems very nice, free, well documented (there is even a book), etc, but which runs only on Windows. Any other suggestion?