Qubes OS
Qubes OS bills itself as "a reasonably secure operating system." It uses hypervisors to provide separation between different domains on your computer. You can make as many of them as you want. They share read-only application software, but cannot write to each other's file storage, unless you explicitly copy between two of them. The windows for each domain are color-coded and identified, in a way that application code can't forge, so you always know which domain you're working with.
Great idea. Haven't tried it yet.
On Twitter @QubesOS.
Available as a 4 gig ISO image or a Torrent. Or on a live bootable USB.
Lots of Asus, Apple, Dell, HP, Lenovo, Sony, and Toshiba hardware have been reported to be compatible.
There's a good half hour overview here (embedded below).