FreeBSD still has a giant lock, which they are slowly splitting into smaller locks right now. And it has already caused several ABI breaks.
I don't know much about Solaris, however I did quite a lot of development on WinNT. It's almost possible to run WinNT4 drivers on Windows Vista there. However, it comes at a great price. For example, filesystem stack in Windows is routinely orders of magnitude slower than in Linux.