Nerval's Lobster writes: If you're a programmer, you're knowledgeable about "big" languages such as Java and C++. But what about those little-known languages you only hear about occasionally? Which ones have an impact on the world that belies their obscurity? Erlang (used in high-performance, parallel systems) springs immediately to mind, as does R, which is relied upon my mathematicians and analysts to crunch all sorts of data. But surely there are a handful of others, used only by a subset of people, that nonetheless inform large and important platforms that lots of people rely upon... without realizing what they owe to a language that few have ever heard of.