The HP-Apollo 9000-425e was in fact the last “true” Apollo in that it was the last system released that could run Domain/OS. If you still have the system, you can emulate an Apollo keyboard and mouse now using an Arduino or something, and install Domain/OS to try it out.
It also fully supports X11 on NetBSD now.
I have a few HP 9000-400 systems (425t, 433s, and 425e) and they run current NetBSD beautifully, even operating fully over the network. Only compiling large stuff from pkgsrc goes slowly due to paging over 10Base-T, as these systems max out at 128MB of RAM. (At least I can use a RAM disk on my server as a swap device at wire speed… Did anyone make a 100Base-T or gigabit card for EISA?)