Zuldi Technology
Stuff we've using/building
Clojure.
Zuldi is fully built with Clojure. We use the 3 official compilers: JVM, CLR & Javascript, and we even made a new compiler that targets ObjC (although we didn't end up using it).
Clojure allowed us to move fast, share code between different target environments and get where we are with a very small team.