My big ongoing project is the Hercules emulator for IBM mainframe systems. Hercules can emulate any IBM mainframe (with one uncommon exception) from the earliest 360 to the most modern z/900, and will run software written for any of those systems. Once upon a time, when Linux first came to the iPaq, Compaq put up a net-accessible compile farm. I tried building and running Hercules on that, but the attempt failed: the system built, but would not run. Well, someone else has succeeded where I failed, and it now runs on the Sharp Zaurus. I'm quite happy to see that, because it means that you can now stick the equivalent of a system that used to take up a large room in your pocket.
I might have to get me a Zaurus...though I'll probably wait till the SL-5600 comes out early next year.