- It runs on the Erlang VM, which is (tech-wise, anyway) fairly old and battle tested. It was deliberately built for resiliency and concurrency. It has some very clever concepts, like supervision trees, cheap processes, interprocess communication via message passing (hey, sounds like OO, right?), and 0 downtime deployments built-in.
- Its creators (namely Jose Valim) come from the Ruby community, and value a lot of the same things Rubyists do: good documentation, testing, and excellent tools for package management, debugging, builds, testing, etc. Several libraries are very similar to their Ruby counterparts. E.g., Phoenix will feel very familiar to a Rails developer. Ditto, the syntax is kind of similar to Ruby. The paradigm is completely different, as Elixir is an immutable, functional programming language. But... aesthetically, they look similar-ish.