4 links
Biseinen.com
biseinen.com
Dedicated to the ever popular "Beautiful man" in Manga, it features shoujo, shounen-ai/yaoi and fan works.
CenterStorm Online
centerstorm.net
Project maintaining several improvisation rounds. Information on participation, archive and forum.
Impromanga World
geocities.com
A place to go if you don't just want to read a manga but help to create a manga.
MK Impromanga
neggie.com
Currently featuring the impromanga Power Force with more planned in the future.