BOND is a cross-platform framework for working with schematized data. It supports cross-language de/serialization and powerful generic mechanisms for efficiently manipulating data. Bond is broadly used at Microsoft in high scale services.
it's written in Haskell and, apparently, faster than protobuf
JIL A fast JSON (de)serializer, built on Sigil with a number of somewhat crazy optimization tricks.
it's written using IL and, apparently, faster than protobuf
But I've not seen anyone yet compare the two, and I can't currently run benchmarks on a dev environment.