What backend technology does WhatsApp use?

News today the Facebook is buying WhatsApp for an obscene amount of money got me interested in which software technologies they use at the back-end, my interest was further increased due to a FB post from Microsoft BizSpark saying that WhatsApp is one of their start-ups, could they possibly use MS technology I wondered?

Well after a bit of searching it seems that WhatsApp uses erlang on FreeBSD!

Erlang is one of the more interesting languages that have become popular of late as it was originally based on my all time favourite – Prolog!