Many, many ACS/OpenACS of all various versions have been run on Sun
E450s and similar machines, particularly back in the dot com boom days
at ArsDigita. An E450 isn't going to give you even nearly the most
bang for your buck (and those old Sun cpus seem to be particularly
slow at integer operations; e.g. gzip'ing files takes a long time).
But if you happen to have an E450 lying around it will run OpenACS