I only worked with rebar(3) so far. Its config format does allow for comments, so there is a small win over package.json.. ;)

the eunit framework gets the job done, too and is bundled into rebar as well as giving you a shell with all your deps and your project code available.

I poked a bit in the sqlite driver so even FFI (called NFI in erlang land, I think) wasn’t as painful as I would have guessed.

So far its age didn’t leave anything to be desired, really and I’m gladly surprised by that, too.

I have yet to try elixir and its mix system. From what I’ve seen it should be possible to pull rebar packages into that as well.