What is GraphQL.NET?
GraphQL is an open source data query language for API's and a runtime for fulfilling queries with the existing data.
This is what the GraphQL Foundation says about GraphQL
GraphQL is a query language for APIs and a runtime for fulfilling those queries with your existing data. GraphQL provides a complete and understandable description of the data in your API, gives clients the power to ask for exactly what they need and nothing more, makes it easier to evolve APIs over time, and enables powerful developer tools.
GraphQL in initial days
GraphQL was initially developed by Facebook in 2012 to solve many issues with their mobile app and was later moved to the GraphQL Foundation in 2018.
GraphQL changes the way how the client communicates with the API to get only the data what it needs. Apart from Facebook, there are plenty of other companies that use GraphQL.
These includes Yelp, GitHub, Twitter, Coursera, Shopify etc. You can know more about the GraphQL customers by visiting GraphQL Landscape page. https://landscape.graphql.org/