I've talked to people at Facebook building their own NoSQL databases for large scale internal use at facebook, working on HHVM, GRAPHQL, working on stuff like t

I've talked to people at Facebook building their own NoSQL databases for large scale internal use at facebook, working on HHVM, GRAPHQL, working on stuff like their location services that serve billions of queries per second. I'm curious, what is it that you've managed to find that's way more interesting than the type of problems only the big four companies have.