Cool stuff
Once upon a time, I built instruments (very special power line analyzers) with these as the main CPU (a 486 with 4MB RAM, later 16MB).
The PC/104 CPU was mount on a mainboard containing all the stuff required for the instrument to work.
Using the PC/104 saved us a lot of work, because we just put in the board and we didn't have to bother with all the PC related stuff (like layout, where to get the BIOS, ...)
First generation booted DOS and DOS/4GW from a flash disk (roll your own style, no fancy Disk-on-Chip) - just to load the software into memory and then take over full control, never go back to DOS.
Next generation booted Linux from a similar home made flash disk, and now we had a decent file system and networking support.
Over time, manufacturer discontinued the PC/104 boards, but newer boards still ran in our system (most of them at least, sometimes we had some compatibility issues to solve).