This is such an awesome idea. It will be interesting to see how many themes you get. I would never have thought of making a marketplace like this because it seems too niche. But I won't be surprised if you prove me wrong!
Shameless plug: I'm trying to get a new community project going, so please consider sharing this on there - http://swym.me/
If there's a market for something, however small, it's always worth giving it a chance because you will always discover new things in the process, things that can often allow you to expand the business beyond what it already is!
Basically, you know how people often ask on HN how did you make that? What stack did you use? It's the same thing, but the tags give you a fun way to find out about other projects built on the same technology. Plus, you might find other creative people you may not have found otherwise.
Thanks! You can add a description to your project after you've created it. I wanted to keep the initial form as short as possible. I will add a description to the tool pages as well.
Shameless plug: I'm trying to get a new community project going, so please consider sharing this on there - http://swym.me/