Prisma is the unbundled version of Graphcool.

Graphcool's main selling point was that everything was hosted: "The Parse for GraphQL".

Prisma's main selling point is that you can host your own database wherever you want and Prisma generates the Schema and TypeDefs for you based on CRUD operations. Compared to Graphcool, you get one instead of two endpoints (Relay and Simple API endpoints are the same in Prisma). Now you can connect your client directly to the Prisma endpoint or you build a GraphQL Server (with graphql-yoga or apollo-server) between your client and database.

All resolvers (auth, file hosting, etc) are written on this GraphQL Server level.

Prisma is a lot more flexible and now also bigger enterprises with legacy databases can use them more easily.

Hope that answers your question. Again, I don't work there but really like their product.