We've been using gRPC since late 2015 for communication between IOT devices and cloud hosted servers. We chose gRPC for the following reasons: bi-directional streaming support; TCP connection multiplexing; mutual authentication with client TLS certs; a large company backing it so that it would likely continue to be supported in the future.
In other words gRPC fit our use case nicely and if it didn't exist at the time we would have built our own crappy protocol ourselves.
I think gRPC is great for server-to-server communication and use cases where you need bi-directional streaming. I would not use it for an externally facing API. I would not recommend it for browser-to-server communication unless you are already using gRPC other places in your stack. If you want the IDL you can use protobufs over plain HTTP.
GraphQL solves a very different problem and I would generally not consider it as an alternative to gRPC.
In other words gRPC fit our use case nicely and if it didn't exist at the time we would have built our own crappy protocol ourselves.
I think gRPC is great for server-to-server communication and use cases where you need bi-directional streaming. I would not use it for an externally facing API. I would not recommend it for browser-to-server communication unless you are already using gRPC other places in your stack. If you want the IDL you can use protobufs over plain HTTP.
GraphQL solves a very different problem and I would generally not consider it as an alternative to gRPC.