Check out [0] and similar projects out there. GraphQL is a query language. It doesn't have to be used for APIs - the Apollo team is using it for state management [1] and others are using it to handle all sorts of non-API data. That being said, it is a Facebook technology released in the context of APIs and it is only three years (publicly) old, so naturally, that is where you are going to see the majority of usage.

[0] https://github.com/apollographql/graphql-anywhere [1] https://github.com/apollographql/apollo-link-state