Interestingly apart from the ruby like syntax they seem to be quite different languages from my limited exposure, in terms of the domains they target (elixir - distributed systems, crystal - whatever go/rust are known for minus distributed systems?), the type system (dynamic vs static), deployment story (elixir - mix based, crystal - binary deployment), the standard libraries they leverage etc.

It seems the sum total of them covers a lot of ground from writing quick CLI apps to large distributed systems for developers familiar with Ruby.