You can use a BEAM system to orchestrate other code, too. As ports, port drivers, nifs, c-nodes, just other OS processes spawned and using IPC/sockets. Lots of options. Using Erlang to supervise an OS process doing work perhaps enhances the isolation principles of BEAM.
To add to that, the BEAM has binaries as a data type so when you're talking to a foreign program you can quickly prototype or design binary protocols once you get tired of parsing/encoding JSON or XML or something at the edges. Depending on the facilities of the foreign language it might be more or less feasible, of course.
