The WonderWitch is an official hobbyist development kit for Bandai's WonderSwan console. It was available only by mail order to Japanese residents. Everything related to the WonderWitch was handled by Qute.
The kit includes Windows software for developing for the WonderSwan, as well as a link cable that plugs into a DE9 serial port, and a special rewritable 128 Mbit cartridge. The cartridge works with standard WonderSwan consoles, and can contain several games, depending on their size. Additional cartridges were also available to buy separately.
The software consists in a C compiler, tools for converting data files, and a utility for transmitting files to and from the console.
The WonderWitch is, for the purposes of amateur developers, a legal alternative to unofficial flash carts popular on other consoles. Those, such as the Wondermagic Color, are indeed much rarer for the WonderSwan than for the Neo Geo Pocket for instance, although the latter machine sold in much lower numbers.
Several programming contests were organized, and some winning games were published in cartridge form and sold to the public, like Judgement Silversword -Rebirth Edition- and Dicing Knight Period.
The only WonderWitch emu known as of now, this emulates the home development kit system for the Japanese WonderSwan Color. Check out the site for more details!This patch for the Japanese version translates it into English.