Unix itself does—seems like a short porting effort compared to the other choices. They had emulation available as well.

A/UX 4.0 I believe was going to be based on OSF/1. The MkLinux port was also useful in the Mach 3.0 migration (as were the open source BSDs which refreshed the 4.4BSD code Rhapsody was based on, from NEXTSTEP 4.0 which only ever shipped as an alpha).