I know Nokia N900 is not yet been sold but there are already some free applications available. For example you can with it play old PC games like Simon the Sorcerer 1 and 2, Revolution's Beneath A Steel Sky, Broken Sword 1 and Broken Sword 2, Flight of the Amazon Queen, Wyrmkeep's Inherit the Earth, Westwood Studios' The Legend of Kyrandia and games based on LucasArts' SCUMM (Script Creation Utility for Maniac Mansion) system such as Monkey Island, Day of the Tentacle, Sam and Max etc.
So if you get N900 when it comes to stores in near future, you can download free application for it from here (might require some technical knowledge):
As this stuff is all free, I thought I could advertise it here. I had myself a chance to try the presale version of N900, and it feels really good in many aspects.