Joyent Slingshot uses Ruby on Rails to create webapps that you run on your desktop that can sync up with the server side. It’s designed to provide an easily installable program for Windows and Mac. This is a good idea and it’s good timing for this product, because it’s coming out head-to-head against Adobe’s Apollo. Apollo could be huge, but it’s just getting going.
For those who have been following my blog, TurboGears was actually extracted from a desktop webapp. I didn’t have a need for the sync part of the equation, but I did indeed create an easy way for me to build Windows and Mac double-clickable apps (with little bits of platform-specific GUI to make it nice).
Good luck to Joyent with the new product! Spiffy stuff!