WonderSwan



The Bandai WonderSwan was a competitor to the Game Boy (interestingly, both were created by the same guy) that never made it outside of Japan, and so it doesn't have many games in English. Much of its titles are anime-licensed and RPGs, but it also has a decent number of (import-friendly) fighters, platformers, and action games.

The WonderSwan comes in three versions: the monochrome classic, the Color, and the Crystal. The Color and Crystal run on the same hardware, but the Crystal has a superior TFT screen and shorter battery life. All of them run on a single AA battery, with the following expected life:
 * Classic: 30-40 hours
 * Color: 20 hours
 * Crystal: 12 hours

There are also AC adapter and rechargeable battery pack accessories for those who'd prefer less battery expenditure.

WonderWitch
The WonderWitch was a full blown development kit with rewritable cartridge, sold via mail order with Bandai's approval. It's basically the official WonderSwan flash cart. While it won't run commercial ROM dumps, there are hundreds of homebrews up on the official site, owing to the WonderWitch Grand Prix coding compos run yearly from 2001 to 2003. Many are of surprisingly high quality, and two (Judgement Silversword and Dicing Knight) were good enough to receive commercial releases on regular Swan carts. Pages for each year's winners are on the Qute site: 2001, 2002 and 2003. There was also a cheaper "WonderWitch Player", which omitted the dev stuff but ran all the same software, but you're going to be paying out the ass either way if you buy one now.