Not at all. The client apps were written in their respective framework/languages. Yes yes, I do believe there's some boosterism going on when their success is

Not at all. The client apps were written in their respective framework/languages. Yes yes, I do believe there's some boosterism going on when their success is entirely attributed to Erlang/FreeBSD alone. Sure the stability and scalability of the backend may have been helped by using Erlang but the fact that they got to scale at all has to do with all these other business/cultural/timing/design factors that I mentioned above. Btw, the one factor I forgot to mention above was the call to use phone numbers as the namespace for user identity. I believe they were one of the early ones, if not the first ones, who eschewed email and/or social login and went straight to phone number. That made them a direct replacement for SMS in large parts of the world where SMS costs were meaningfully expensive to the population. One more example of focusing outside the US market in general and outside of Valley bubble in particular.