Erlang term storage - a queryable database for your processes to store terms in.
Manually raising exceptions, handling them, defining your own, and using them idiomatically.
mkdir; rmdir; mkdir_p; stat; open; stream!; read; stream_to!; regular?; touch; rm; write; rm_rf; write_stat
Elixir's new package manager.
Finishing the addon, publishing it to npm, and setting up CI.