Whoa.... I seem to have checked almost all of the boxes, and "other" covers a multitude of sins (various Win server OS's, OPENSTEP, Solaris).
Mebbe I need to get rid of some of this hardware cluttering up the place.....
...... on second thought, naaah... 😛
FWIW Leopard is my primary OS both here and at work. XP/Vista are used for the odd work-related application that is Windows only (XP mostly on native hardware, Vista under VMWare). I run a couple of Windows servers to keep my hand in (I'm a systems admin working with both Windows and Mac), I have an old G4 running Tiger server (file/media server), an old Mac Plus (just a toy, really) and a Linux box (mail/web/bitlbee servers). The solaris box is getting old, but is basically a backup for the Linux machine and OPENSTEP is "just because." =]