Ask HN: I have a great idea. Where can I get feedback before going further?

So I have had this idea for a while now about an app/website that would target a large niche community (programmers+gamers). I have a proof of concept. Now I would love to get some feedback about the project from multiple people before getting too much involved, or getting other people involved: "Would people be interested in it or will I die trying to build up a community? Is there something similar online that I might have missed? etc."

What are some good places to get that type of public feedback?

I'd hate to spend 6 months in the dark building this thing to realize that it already existed, or that noone is interested in it.

Thanks!