You missed one
You did not mention OS/2 Warp Server.
And you can stop your sniggering at the back.
This has been managing my (small) office network for 10+ years from the same hardware - a Pentium Pro IBM machine with scsi disks. A mix of OS/2 and Win desktop and laptop clients.
I said... "stop sniggering!!!"
Up time? I dunno. Months. Years maybe. Last time I re-started I don't remember but was probably when the building management wanted to check the aircon system at the weekend. Should I even know this if my server does the business?
Oh yeah I've peed around with other systems. Latterly Mac OS/X Server. Does what OS/2 server has been doing without maintenance for years.