WebTechnology used to develope Stakeoverlfow?

Which web language or technology is used to develop stackoverflow, to make its website such dynamic to handle lot of data?

Reason being, while discussion for creating website for one of our client, we want to do analysis of how it would be feasible to create same as stackoverflow.

Question

1. Which Web Technology used?
2. Programming language used?
3. Design patterns implemented?
4. Which database is used to store data and why the selection of DB?
5. Any other advance technology used?
6. Any independent platform developed only for stackoverflow?
7. Why at Google search for any technical problems, we find stackoverflow as the most suggested results, is there any technology used?
8. What is so important in UI design, I feel its simple, dynamic, accessible, neat?

Thanks in advance for answers. as it is going to help us in building similar design.