GRiSP runs on an RTOS using POSIX compatability. So baremetal-ish? Still you can apparently program RTOS tasks and control them from Erlang land. :-) Also Nerve

GRiSP runs on an RTOS using POSIX compatability. So baremetal-ish? Still you can apparently program RTOS tasks and control them from Erlang land. :-) Also Nerves supports the GRiSP board itself not the RTOS; pretty sure Nerves runs it using Linux IIRC.