Update #2: kmg has released PSwan v0.03 today with source code, and REi has also updated his own WS emulator port to OSwan v0.01. Please note all related changes and updates are included in the ReadMe files of each release.
Update: kmg has now released his version of the WonderSwan Color emulator PSwan v0.02 complete with source code. Changes include SRAM saving support and also 16MB ROM support as well.
REi has released OSwan v0.0 today, a WonderSwan Color emulator port of v0.7 for the PSP handheld! Currently speed is decent for non-color games and slower for the color titles. At the moment there is no sound or save functionality present, but all things considered not bad for an initial release! To compliment the OSwan release, Shylph has released this WSC File Selector.