Rockin-B released a Wonderswan Emulator for the Sega Saturn, heres the info:
Ported by The Rockin'-B (version 05/01/28) http://www.Rockin-B.de
Read carefully to avoid problems!
- runs VERY slow
* only Master CPU is used
* graphic rendering in software
- no sound yet
+ frame skipping
+ minimal CD browser for loading roms
- no zipped roms yet
+ extended RAM Cart support:
only 4MB RAM cart allowes playing games
bigger than 1MByte up to 4MByte
(1MB cart does NOT SUPPORT this)