Windows NT and NetWare on PA-RISC, and a HP-UX port to x86
Back when I was working on my article about PA-RISC, HP-UX, and UNIX workstations in general, I made extensive use of OpenPA, Paul Weissmann's invaluable and incredibly detailed resource about HP's workstation efforts, HP-UX, and tons of related projects and products. Weissmann's been doing some serious digging, and has unearthed details about a number of essentially forgotten operating system efforts.
First, it turns out HP was porting Windows NT to PA-RISC in the early '90s.
Several magazine sources and USEnet posts around 1993 point to HP pursuing a PA-RISC port to NT, modified the PA-RISC architecture for bi-endianess and even conducted a
Paul Weissmann at OpenPAback-roompresention at the '94 Comdex conference of a (modified HP 712?) PA-7100LC workstation running Windows NT. Mentions of NT on PA-RISC continued in 1994 with some customer interest but ended around 1995.
The port eventually fizzled out due to a lack of interest from both customers and application developers, and HP realised its time was better spent on the future of x86, Intel's Itanium, instead. HP also planned to work together with Novell to port NetWare to PA-RISC, but the work took longer than expected and it, too, was cancelled.
The most recent secretive effort was the port of HP-UX to x86, an endeavour that took place during the final days of the UNIX workstation market.
Parts of the conversation in these documents mention a successful boot of HP-UX on x86 in December of 2009, with porting efforts projected to cost
Paul Weissmann at OpenPA100M+between 2010 and 2016. The plan was for mission-critical x86 systems (ProLiant DL980 and Superdome with x86) and first releases projected in 2011 (developer) and 2012 (Superdome and Linux ABI).
I'm especially curious about that last one, as porting HP-UX to x86 seems like a massive effort during a time where it was already obvious Linux had completely obliterated the traditional UNIX market. It really feels like the last death saving throws of a platform everybody already knew wasn't going to make it.