Recently Opened Hand announced Poky Linux for embedded devices. Currently the system runs on various Sharp Zaurus devices and there is also experimental support for Nokia N800 and OpenMoko Neo1973 devices. I tried the Poky system on qemu and also installed it on my Nokia N800.
The system contains UI component called Sato, which is corresponding component to the Hildon widget set. The system is fully open, and contains currently basic applications such as web browser and video player, a PIM suite called pimlico and some games.
Here's a capture of Poky Linux running in qemu:
And the system running on Nokia N800:
Seems that network is not supported yet on N800 so I was not able to test the browser any better. But currently the Poky Linux seems a promising option.