Most PDAs run Pocket/pc, a.k.a. Windows Mobile.
This comes with a cut-down version of Excel, and there are various aviation programs for it, many of them free.
I use an HP4700 PDA with a paid-for prog called Flightcalc. Like nearly all of them it is US-centric but one wouldn't use it for flight planning. It does all the calculations and does a nice graphical W&B display.
The only problem with PDAs used infrequently is that quite often the battery is found to have gone flat....