MochiAds
Apparently MochiAds is built using everything but the kitchen sink:
For the technically inclined, the UI for MochiAds is built with Pylons, Genshi and SQLAlchemy. The secret sauce is a combination of Python and Erlang code, and we’ve got Nginx as the gatekeeper. I’ve got nothing but good things to say about this whole stack. Erlang’s module reloading, concurrency oriented programming model, and pattern matching has really been a dream.
Heh. Cool.