Inspired by the BeOS, Haiku looks almost exactly like the older operating system, featuring the trademark yellow tabs atop floating windows, featuring a Linux-like terminal, and true multi-threading to take advantage of multiple processors.
And the Haiku project is more than a series of intriguing screenshots. You can actually run the project today, by downloading a virtual image from their Web site, popping into VMware, with or without a full set of applications, from Mail to Firefox to a PDF viewer and a Paint application.
I downloaded the VMware image with the latest nightly build, and sure enough... 1996 all over again. But it wasn't an OS running on a Zip Drive on a 603 or 604 processor. It was a virtual machine running on my MacBook Pro. Quick. Fast. Elegant. Not very useful, of course, but an interesting science project. It works.
So if you want to toy around with an elegant OS and you want to kick the tires or just scratch that nostalgia itch, check out Haiku. See also: OS News: BeOS Lives: Haiku Impresses.