I'm into 8-bit stuff myself, not exactly what most of you are thinking of, but some of you might be shocked to learn how much 8-bit Unix stuff there is.
My favorite is the Tandy Color Computer 3. Not well known because it's predecessor stuck with early 80's hardware through the mid 80's, the CoCo 3 completely blows away the competition (Atari 130XE, Commodore 128, Apple IIc, even the IIgs) because it just happened to use the Microware (not Macintosh) OS-9 operating system. It starts up in disk basic like everything else, but insert a floppy and type DOS and it comes up in an only slightly non-standard Unix. There are utility packages that add more standard Unix commands, lots of applications,and an optional GUI, but what's most amazing, FULL MULTITASKING!!! That's right, five years before a 640k Commodore 128 could even have two GEOS windows open, the 512k CoCo 3 could have up to eight, a GUI as good as GEOS, and four users at once. Of course pushing it's limits like that slowed it down, but just playing Koronis Rift while downloading from Compuserve at the same time, while someone else copied a spreadsheet to the Model 200 was pretty amazing.
Today, the HD6309 CPU and NitrOS-9 OS upgrades make it much faster.
Unix clones and variants are now available for the Apple IIgs, Commodore 64, and probably many others, so if you have trouble finding the 68000 or ARM systems from the good old days, try something that was a little closer to home. There is probably a Unix of some kind for whatever you used to use.
Of course, the 65802 and 6809 are not 68000's, but isn't the challenge of pushing the supposed limits a huge part of the fun of retrocomputing?