[wikwocket]

The concept is decently clear, at least to hackers like us who regularly have side projects. Your tagline is good, which is very important for new ideas.

However, I'd say the landing page is a bit light on details (you want a short page to simply capture emails, but you also want to communicate value). Also, the background color scheme is a bit garish and distracting IMO. Finally, as 6thSigma mentioned, "marketplace" does denote buying and selling. I guess other terms you could use would be forum, board, community, etc.

If you are not aware of it, you could look to the /r/SideProject/‎ subreddit for ideas/inspiration.