Most people don't think of them as computer systems, but late-90s and early-2000s phone and PDA OSes. Specifically, EPOC32/Symbian, Apple Newton, BlackberryOS,

Most people don't think of them as computer systems, but late-90s and early-2000s phone and PDA OSes. Specifically, EPOC32/Symbian, Apple Newton, BlackberryOS, PalmOS, Qualcomm RexOS, and Windows CE/PocketPC/Mobile (and its later incarnation Windows Phone/10 Mobile) Newer calculators, like the TI-Nspire Cx-series and HP Prisms. Proprietary non-linear editing systems from the 80s and 90s before the switchover to software. A few legacy systems that haven't quite been emulated yet are BeOS, and RISCOS, certain proprietary Unix implementations like A/UX, Amix, Irix, NeXtOS, Apollo DomainOS, AIX, PA-RISC, Ultrix, etc., and Japanese PCs like the PC-98, PC-88, Sharp X1, Sharp X6800, and FM-Towns Minicomputer hardware, like VAX Machines, DEC Alpha Systems, and DECstations, are also lacking in good emulation, but the OSes (OpenVMS and Ultrix) are available to hobbyists. Itanium has not so far been emulated, so IA-64 versions of Windows are probably going to be lost (as no more IA-64 processors are being made) should nothing be done.