I used gRPC for numerous hobby projects during my undergrad to glue together binaries running in different languages (e.g. a simulation server running in C++ and a scripting client in Python). By passing around a shared data structure (Protobufs), one does not need to waste time writing serialization/de-serialization adapters. It is also useful for gluing together microservices.
FB's Thrift also solves the same problem, and is an alternative to gRPC.
Going into the microservice aspect above, it provides a nice abstraction of remote function calls, so that you can write microservice code that looks like it's executing a local function, but is really just expecting a remote server to implement the method name. In general, that's just RPC calls though. Google's implementation has proven very intuitive to learn, and has a nice size community online for help debugging, etc.
FB's Thrift also solves the same problem, and is an alternative to gRPC.