We do have a (yet unused) marketplace on our own forum:
http://teamaircoin.org/forums/forum/market-place/ also.
What do you mean by different versions? Something like Bitcoin/Litecoin, where one coin is "gold" and the other "silver"?
P.S: I want to thank the Dev-Team for the professionalism and the energy you put in EVERY post here in this thread. I've never seen this kind of commitment from other Devs. You really take the doubts of the Aircoin community serious, and answer all our questions! The politeness of this community also baffles me. Thank you all! It's always a pleasure to visit this thread and to read all the posts.
Yes, something like the Bitcoin / Litecoin relationship.