Hi, Scott.
My recollection is that I tried to port GNU coreutils to get GNU date for Solaris. I was not successful.
It might be useful for the community here to have someone (with more expertise that I have) do a port. Judging from the posts here, I would say for Solaris and AIX, possibly HPUX.
I never found anything in sfw in Solaris to handle date arithmetic, but it's possible I missed something -- it was years before I stumbled on sfw
I figured if the Sun/Oracle folks couldn't do the port, then it was probably difficult, or required a
lot of extra work. The stuff in sfw seemed mostly like stand-alone items, e.g.
ggrep ... cheers, drl