Warning: The Kindle's not actually robust enough to run arbitrary code, and it's very easy to crash your device by doing the wrong thing --- e.g. while (true); will do it. (Can't break out of infinite loops.) So be careful, and when you device crashes and loses all your data, don't say I didn't warn you.
If you want to hack it, get the source code. Some things you might want to pull out of it include:
- Retroweaver integration, allowing Java 1.5 language features (generics! autoboxing! foreach loops!) on the Kindle's 1.4 JVM.
- com.cowlark.eventbus, a port of GWT's excellent event bus system, and a wrapper around the Kindle lifecycle APIs so that we don't need to worry about what thread they're calling into our application from.
- com.cowlark.kterm, a slightly-complete VT52 terminal emulator with crude but serviceable custom inputmethods allowing actual code to be written in it... although with four shift keys it does feel a bit like a ZX Spectrum.