QNX- its a microkernel, its a dessert topping

The QNX realtime platform is now available for download! Before we launch it to the world on Tuesday, we're giving our pre-registrants first access to the FREE download - available now at http://get.qnx.com
With the platform, you'll get the QNX Neutrino microkernel RTOS, Photon microGUI windowing system, OS modules and utilities, Voyager web browser, multimedia support for MP3, RealAudio/Video, Flash, MPEG, CD Audio, a Quake III demo that lets you play the commercial version if you have it installed, lots of public domain ports, and much more.