Haiku is a FOSS operating system inspired by BeOS. It’s not very useful as of yet, but it shows good progress. Haiku is also proof that C++ can work in the kernel.
Haiku (and BeOS) is noteworthy in a KDE context simply because
pretty much all some of what Nepomuk tries to achieve, BeOS already did 10 or more years ago.
Among other things, new features compared to include a WebKit browser, WLAN support, and internationalization support.
And now fire VirtualBox up and give Haiku a spin.