Tru64 UNIX 5.0
Tru64, formerly Digital UNIX, formerly OSF/1 was DEC's UNIX product for their line of Alpha based systems. After DEC's acquisition by Compaq, it was renamed to Tru64. DEC previously had sold a BSD derivative named Ultrix for Vax and MIPS based systems. Their new UNIX on Alpha was meant to counter AT&T and Sun's SVR4 Unix. Tru64 / DIGITAL UNIX / OSF/1 is somewhat interesting in that it used portions of the Mach microkernel and BSD kernel and userland in a manner not entirely unlike NeXTSTEP or Mac OS X. Like OS X, Tru64 itself is not a microkernel system but uses Mach code in its kernel to implement threading and scheduling and possibly other features.
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There are people all around who can help with such things. You might also ask around on the VCFED forum: https://www.vcfed.org/forum/forum lots and lots of people there who deal with DEC stuff.