If a 20-year old computer is not your thing (see the Oric-1), then how about a 15 year old operating system? Here is QNX2.25 (circa 1989/1990) running on an original Pentium MMX 233Mhz laptop. The display shows QNX2.21, but I don't think the version number was updated. Pentium Pro is too new for this version of QNX, which was made to run on 286+ systems, with support for TiB of RAM and disk even when it was written. January 2004 for my Operating Systems course. It only sees 640k of memory (the laptop has 64Mb), as the chipset isn't properly supported. However it runs perfectly smoothly in realtime, per the QNX design specifications.