Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
I really love the theme used for this exchange. Is there any resource that could be reused or some reference (fonts, graphics, css, ...)?
The main font of the site is Whiteboard Regular, and as far as I know you can use it freely in your projects.
Everything else is copyrighted by Stack Exchange. You'll have to contact them directly ("contact us" link in the footer) to discuss what you can and cannot use.