A pretty comprehensive discussion of what makes the Stack Overflow model of sites unique is contained on the "About" page for each site.
You can use Stack Overflow's as a model: About Stack Overflow
We don’t run Stack Overflow. You do. Stack Overflow is collaboratively built and maintained by your fellow programmers. Once the system learns to trust you, you’ll be able to edit anything, much like Wikipedia. With your help, we can build good answers to every imaginable programming question together. No matter what programming language you use, or what operating system you call home – better programming is our goal.
Stack Overflow is as frictionless and painless to use as we could make it. We believe finding the right answer to your programming questions should be as easy as falling into the pit of success … and maybe even a little fun along the way.
So What? Who cares? Isn't this just like a dozen other websites?
What’s so special about this? Well, nothing, really. The only unusual thing we do is synthesize aspects of Wikis, Blogs, Forums, and Digg/Reddit in a way that we think is original.
Stack Overflow is that tiny asterisk in the middle, there.