Er.js: Erlang-in-JavaScript

Erlang's two most important features are finding their way into many languages:

- Message passing with mailboxes and pattern matching receive statements

- Supervision trees, allowing the separation of function code and error handling

I hate quoting myself but:

Any sufficiently complicated concurrent program in another language contains an ad hoc informally-specified bug-ridden slow implementation of half of Erlang.

With all respect to Greenspun.