And we can tell our kids we had this thing called endianness which showed up in structure packing, system calls, network byte ordering, and hopefully portable binary file formats. Thankfully we had RPC and IDL to save us from that mess... not.
Oh and don't forget the windowing system war on top of the Unix war, all with different desktop and library concepts: CDE, Motif, Openwin, NeWS, DM, X11 and X10 at least.
One compatibility honorable mention goes to Apollo for at least making an attempt at flavor normalization: you could have an env var that would resolve a symlink at every file access near the top of the filesystem, where there would be a collection of different BSD/SystemV/Aegis(?) all running at once. [2]
1. https://maultech.com/chrislott/resources/cstyle/ifdefs.pdf
To this date, this is the only network protocol I have ever seen that not only allowed you to choose the endianness you will use in the header, but also the floating point format.
Don't forget AIX/ESA (a weird beast), NextSTEP (which is still with us, in disguise), the HPC crowd (UNICOS, OSF/1 AD...), SINIX (my first contact with the internet, thanks to Siemens/Nixdorf)...
Having to deal with three variants is relatively simple.
Now having to deal with DG/UX, Aix, Tru64, SGI, HP-UX, Solaris, BSD and the new incumbent Linux, that was fun.