The IBM WorkPad z50 is a NEC VR4121 based PDA. It comes with WinCE in flash.
+ 131Mhz NEC VR4121 SoC + NEC VR4171A Companion chip + 16MB RAM (Expandable to 48MB) + 4MB Video RAM + ITE IT8181F Video controller + Rockwell RP336LD Modem
There is a netbsd and a (unmaintained) linux port available
Useful info and datasheets on various parts used in this machine can be found at http://www.eecg.toronto.edu/~lemieux/z50/