The GNU Compiler Collection (GCC) had a backend for S/370, but it became obsolete over time and was finally replaced by the S/390 backend.
This causes Mathomatic to crash when used with the new LLVM backend, which doesn't seem to like the standard C library function memmove(3).
Movim (Official Pod) a distributed web-based social platform, which uses Metronome as backend.
An important implementation favored for its processing speed and power is the Theano computational library backend.
WISfans provides backend analytics and CRM club marketing to teams in order to leverage engagement and growth, too.