Pretty cool: http://code.google.com/
Google engineers are encouraged to spend 20% of their time (i.e., one day a week) on personal projects, which often end up being Open Source. This, and other code developed inside Google may now be found on those pages, with more coming. I think that is an excellent initiative.
I know that Google uses MySQL for various things too, with some custom mods, so perhaps those will pop up as well 😉