Windows Mobile/CE users can enjoy NetHack with the official 3.4.3 release for PocketPCs.

I've logged countless hours playing it on my aging HTC 8125. The 8125's keyboard lends itself well to playing roguelikes, and the keyboard HUD allows for play using only the stylus.

You can pick up an 8125 on eBay for ~$150 these days.

Alternatively, the ludicrously rich could buy a $20 bottle of water from Charity Water [charitywater.org] and provide clean drinking water for a needy individual for the next twenty years.