Support across languages etc is much less mature but I find thrift serialization format to be much nicer than protobuf. The codegen somehow manages to produce types that look like types I would actually write compared to the monstrosities that protoc generates.

Something like MessagePack or CBOR, and if you want versioning, just have a version field at the start. You don't require a schema to pack/unpack, which I personally think is a good thing.

CBOR is probably the best and most standards compliant thing out there that I’m aware of.

It’s the new default in a lot of IOT specs, it’s the backbone for deep space communication networks etc..

Maintains interoperability with JSON. Is very much battle tested in very challenging environments.

There are none, protobufs are great.

Mentioned above: https://github.com/stepchowfun/typical