"WonderSwan is a handheld game console released in Japan by Bandai on March 4, 1999. It was developed by the late Gunpei Yokoi's company Koto and Bandai. The WonderSwan was made to compete with the Neo Geo Pocket Color and the market leader Nintendo's Game Boy Color (even though the developer for the WonderSwan, Gunpei Yokoi, developed the original Nintendo Game Boy).
The WonderSwan was later replaced by the WonderSwan Color; although, some WonderSwan Color games are compatible with the original WonderSwan, many are designed exclusively for the WonderSwan Color and show a message such as "This cartridge is for WonderSwan Color only" when run on the original WonderSwan.
The WonderSwan was available in ten case colors, playable both vertically and horizontally, and features a fairly large library of games, including numerous first-party titles based on licensed anime properties, with significant third-party support from Squaresoft and Capcom. As it was a console designed essentially for the Japanese market, most of the games are in Japanese, with only a few featuring English text."
Source: Wikipedia, "WonderSwan", available under the CC-BY-SA License.