YAME works great for me - good luck trying to find it though

. I have the Cassiopeia EM-500 - buttons are sort of layed out like a GameBoy and let you press more than one at a time. I play GameBoy, GameBoy Colour, and NES games with it. It also emulates TurboGrafx16, but the EM-500 is too slow to play TG16 games properly.
If you're one of the poor saps with an iPaq, good luck at playing games as they only accept one button imput at a time. Unless you get the GameBoy add-on controller, so you can REALLY make it look stupid

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Odonadon