Ever needed to test something out but didn't want to use your own machine? JPC-2 solves that problem by giving you a virtual machine in your browser that's capable of running Windows XP (with or without Office), Ubuntu 6 and Ubuntu 8.
Running these virtual machines from your browser is, in some ways, a gimmick. Technically you're downloading a Java applet that's doing the heavy lifting. That said, what you're not doing is setting anything up or installing an operating system. You're simply downloading the necessary files to run a disposable, virtualised copy of XP or Ubuntu for testing purposes (or maybe to run that one Windows app you can't get on your Mac). Whatever the case may be, it's a good tool to keep bookmarked for the next time you need it. Getting started is a bit slow, but you can just let it run in the background while it downloads the necessary files and run your tests when it's ready. Once things are up and running it is surprisingly responsive and can run whatever you'd find in a standard installation.