GraphQL is a query language for your API and a server-side runtime for executing queries by using a type system you define for your data. GraphQL can be integrated into any framework like ASP.NET, Java, NestJs, etc and it isn't tied to any specific database or storage engine and is instead backed by your existing code and data.

Basic and advanced samples - simple 'Hello GraphQL!' example based on console version from GraphQL for .NET on GitHub, but using ASP.NET Core, Entity Framework Core and some best practices, patterns and principles. Advanced - GraphQL queries and mutations with full 'Star Wars' database

GraphQL is a single API face for different clients like mobile, desktop apps, tablets… It’s built by Facebook.