Haiku is all new source, so they had to figure out how to get the binaries to run. I am not the POSIX expert, but I think it was just an API guarantee not ABI.
There were several companies that had the BeOS source and that source can be found in the wild. It is speculated that yellowTAB ZETA was based on unlicensed BeOS source code.
There were several companies that had the BeOS source and that source can be found in the wild. It is speculated that yellowTAB ZETA was based on unlicensed BeOS source code.