Somebody please correct me if I'm wrong, as I'm still reading the readme and the code, but I think Elixir is closer to Erlang (the language) intents, being immutable and 'more functional'. Reia has some object-orientation built in, with stateful objects and "types" that mix data and code.

Here's a very good blog post by Reia's author talking about the 'non-Erlang' things in Reia: http://www.unlimitednovelty.com/2009/03/is-reia-object-orien...

I personally think that they're both amazing from what I've been seeing. I gotta dive-in more and do some tests, but it will be a joy to see Erlang getting more adopters. :D