The website where MantaRay was previously hosted (www.mantamq.org) seems to have died. There does not seem to be a Coridan anymore. And there's no download here at SourceForge. Ergo, is MantaRay a dead project? I've tried to contact the developers, have not heard back, so I figure I'll try this route: claim it dead and see if anyone screams.
And than if you need more details please let me know.