This is process registry similar to gproc. The difference is that gproc complete handles the logic of mapping key to pids and vice versa. Regine on the other hand only deals with the association of key to pids. The reverse direction and some other mapping functions have to be supplied by the developer through a callback module.
This the developer to full flexibility to implement mapping models that to not fall into the one key, one map model.
Using rebar3:
# rebar3 compile