(I don't know of any, though)
The original FLAC format includes a very thin transport system. This system of compressed FLAC audio data mixed with a thin transport has come to be known as 'native FLAC'. The transport consists of audio frame headers and footers which contain synchronization patterns, timecodes, and checksums (but notably not frame lengths), and a metadata system. It is very lightweight and does not support more elaborate transport mechanisms such as multiple logical streams, but it has served its purpose well.The native FLAC transport is not a transport "layer" in the way of standard codec design because it cannot be entirely separated from the payload. Though the metadata system can be separated, the frame header includes both data that belongs in the transport (sync pattern, timecode, checksum) and data that belongs in the compressed packets (audio parameters like channel assignments, sample rate, etc).