The internal GCL language, as well as its failed replacements. There's a nice introduction in this paper: https://pure.tue.nl/ws/portalfiles/portal/46927079/638953-1.... Back when I worked there, I actually quite liked the syntax of the language, though the semantics of the language was quite a dumpster fire.

Another internal language for querying Monarch. See section 5.1 of http://www.vldb.org/pvldb/vol13/p3181-adams.pdf