Ubuntu: Want to try out the latest build of the next Ubuntu release with almost no hassle at all? TestDrive is a one-shot tool that downloads, virtualises and keeps daily Ubuntu builds up to date.
TestDrive runs from the command line, but you literally enter only one number to make it work. Run it from your Applications/System Tools menu, and a terminal prompt asks you to pick which daily build of Ubuntu you want to install. Enter your number, hit return, and TestDrive gets to work downloading the latest ISO, turning it into a virtual machine, and then, if you have VirtualBox or KVM installed, launching it immediately.
The truly great part of TestDrive is that when you run it again, it uses the rsync command to see what's changed in the daily build on Ubuntu's servers, grabs only those changed bits and downloads them, then re-compiles your virtual machine and launches it anew. If you want to change the memory and other settings TestDrive uses to set up its virtual machines, you can edit the /etc/testdriverc file, but the defaults are pretty sensible.
It would be icing on some tasty cake if this tool could be made to work for Windows users. If that can be pulled off, or there's a similar tool, do let us know in the comments. In the meantime, it's a free download for Ubuntu users, who can install it by running the command sudo add-apt-repository ppa:testdrive/ppa, then reloading their sources and installing the testdrive package.