I like CBOR (http://cbor.io/). It's a standard (RFC-7049), it can encode 64-bit integers, IEEE floating point, text (UTF-8), binary data (anything non-UTF-8), booleans, null and undefined. You have arrays and maps (and maps can have any value as an index, not just strings) and you can semantically tag data as well. The RFC is one of the better RFCs I've read, covering all the details and plenty of encoding examples to test against.