At work:
Several OS incl. Solaris, OS400, Netware etc.

At home:
SuSE 7.0 (web, mail etc, dmz)
PC-DOS 7.0 w/Windows 3.11 under OS/2 Warp (nostalgia).
FreeBSD as Firewall and router.
Win2000 just because my friends demands it :-).
And finally Netware as fileserver.