Yeah, keepass2 works w/ mono. I have it installed on an xubuntu system. There's an official package (in universe).

keechallenge is also supposed to work w/ mono. That said, at least on my machine the fonts in keepass2 are rendered too small, making the application very difficult to use. I spent about an hour trying to figure out how to fix them and could not, so I have not tried setting up keechallenge there.