Most internal projects run of private Mercurial repositories
Engine being Open Source, just made sense to use GitHub.
For task management (Celery) and shared sessions.
Used to be MySQL, but once moved to MongoDB, everything just speed up dramatically, data became pretty and easy to work with. Sophisticated aggregations allow us to run complicated analytics anytime as easy as possible.
Most static stuff and published games run from S3.
Almost all our servers run from Ubuntu on AWS EC2, as it is robust and easy to work with.
More new stuff been made with node.js especially real-time bits.
Most back-end made with Python + Whiskey, combined with some node.js.
Used to be Apache, but configs, robustness and performance of nginx - obviously made sense.
And we regret using it.
StackExchange style board