They are basically an OS, with containarized applications.
Thanks to them I stopped caring about the underlying OS.
Elixir has a lot in common, but it takes it to another level. You can call functions from those other applications on the server with nothing more than a Module.function(arguments). You can call a function on another node in the cluster by just sending the node + module, function and arguments.
Because of immutability and message passing, this just works everywhere. With Java, a similar implementation would have to guard against memory references and mutex locks that wouldn't behave the same way on different nodes.