sometimes Protocol Buffers, and now FlatBuffers, and possible "next thing" :)
Most of Google's (and other) services are internally running on Protocol Buffers.
FlatBuffers is simplified, faster version of Protocol Buffers format.
Like Cap'n Proto and SBE, it supports “zero-copy” deserialization, so that accessing the serialized data does not require first copying it into a separate part of memory, which makes accessing data in these formats much faster than data in formats requiring more extensive processing, such as JSON, CSV, and Protocol Buffers.
It is the data serialization format used internally in Facebook's Android client, replacing JSON; in that role, they credit it for dramatic performance improvements in the client.