Ask HN: What programming language was ______ written in?

I am curious as to what programming languages were used to make various products and thought it would be interesting to keep a running list of as many as we could.

Feel free to list as many as you can in the comments section and I'll try adding it to the master list. Or you can ask about one and hopefully someone will answer.

  Facebook   - PHP and C++
  Mac OSX    - C and Objective C
  iOS        - C and Objective C
  Windows    - C++, C, and C#
  Linux      - C
  Android    - C
  Google     - C++, Python, Java
  Dropbox    - Python
  NSA        - Python
  Yelp       - Python
  Quora      - Python
  Youtube    - Python
  Slide      - Python
  NASA       - Python
  ...