There's a lot of Girl Genius stuff on AO3. The Foglios (authors) seem okay with fanwork existing (there's even a fanfic-discussion channel on the semi-official

There's a lot of Girl Genius stuff on AO3. The Foglios (authors) seem okay with fanwork existing (there's even a fanfic-discussion channel on the semi-official Girl Genius Discord server). Of course, stuff on AO3 doesn't make money, which may be a sticking point.