gRPC
gRPC is basically Google's official RPC implementation for Protocol Buffers (in particular for proto3), but released as a separate project.
Building on the HTTP/2 standard brings many capabilities such as bidirectional streaming, flow control, header compression, multiplexing requests over a single TCP connection and more. These features save battery life and data usage on mobile devices while speeding up services and web applications running in the cloud.
See the motivation and principles of gRPC, and a review in LWN