Safari is based on the KDE browser's open source rendering engine, however. I don't know how much of it is left but certainly it was a huge boon for them -- and

Safari is based on the KDE browser's open source rendering engine, however. I don't know how much of it is left but certainly it was a huge boon for them -- and later Google -- to start with a highly standards-compliant and open code base. I've found the best OS projects are system libraries and utilities and tools where the developer is also the end user. The more UI is piled up, the more non-developer involvement is needed the worse it gets. The worst are open source games; nothing good since Nethack.