GitHub has always exposed raw source files in public repos via the raw.github.com domain, but — presumably for security reasons — they serve most files with a text/plain content type. This prevents all browsers from rendering HTML, and prevents some browsers from executing JavaScript and CSS.
I've always thought this was unfortunate. Being able to point directly to raw files in a GitHub repo can be useful for testing and for quick demos. I especially want it when I'm writing jsPerf tests and want to compare the performance of code in different branches.
So I threw together rawgithub.com.
It's essentially a proxy for raw.github.com that serves things with the correct content type based on the file extension. Just replace raw.github.com in any GitHub URL with rawgithub.com and you can render HTML, execute JavaScript, and apply CSS right from your GitHub repos.
Have fun with it, but don't use it for anything important! It's slow and it might break occasionally.
Oh, and the source is on GitHub, naturally.