[1letterunixname]

I remember having BootCommander on a test box containing Windows 95 (and a bunch of other crap) to boot to up to 16 OSes.

Back in the day, university campus networks popularized a "cluster" approach of logging in to specific machines whereby hosts followed the pattern: $(uname)[0-9]{2}. You would soon setup authorized_keys and a script that would check the load of all machines by iterating ssh. The same home directory would be shared to all machines, regardless of OS, so portability of shells scripts and POSIX/C code was necessary.