Pretty much everything, honestly. Erlang was built from the start to accommodate massive concurrency and robustness requirements, in particular for telecom switches, but largely applicable to anything.

Node's a single-threaded reactor pattern event loop, whereas Erlang/OTP is an SMP-enabled virtual machine with a preemptive scheduler that manages lightweight actors called processes, all isolated from each other with their own stack and heap, that can be cheaply spawned and communicate only via message passing. On top of that, Erlang offers location transparency for processes and easy node distribution out of the box. OTP then provides a framework for fault tolerance and reusable components by supplying generic behaviors (server, FSM, etc.), supervisors for monitoring and restarting processes when they crash, endpoints for hot code reloading, and more.

You should try it one day. There's really nothing else like it, even if its underlying concepts aren't necessarily novel - but they're well combined and largely obscure in mainstream practice. A lot of platforms have tried to implement their own equivalent actor model approaches (Celluloid for Python, Akka for Scala...), but none reach the same level.