Slang is a proprietory language developed by GS, it's been around for ~15 years I think. If I remember correctly they have a development/analysis environment called SecDB in which all coding is done with Slang. All their modelling, pricing and risking is done in SecDB across all asset classes so it's pretty widely embedded.
I've looked at Slang a bit. It's an interpreted dataflow language running on an in-memory database called SecDB. Untyped, Pascal-ish, single-threaded, and poor support for namespaces. Like a spreadsheet, it only needs to recompute the subgraph that has changed. It was probably innovative 25 years ago (I think it came out mid-80s), but today you could write Java code and use memoization aggressively to speed things up…
http://adgrok.com/why-founding-a-three-person-startup-with-z...