Apparently a lot of telephone switches used neokernels. Ericsson's AXE series telephone switches ran software written in their proprietary PLEX language, and th

Apparently a lot of telephone switches used neokernels. Ericsson's AXE series telephone switches ran software written in their proprietary PLEX language, and the PLEX runtime and the AXE OS were basically the same thing. That helped reduce overhead for context switches between tasks: hardware address spaces didn't need to be switched, or even supported; the runtime handled task separation. Erlang was meant to fill this role in newer switches, but it looks like PLEX is still being developed and used.