Now = already EOL, Soon = within the next 6 months, Later = by the end of the year
Windows
235 now: 87 Win 7, 17 Win2008, the rest are Win10 up to 20H1/2004, and a handful of unfortunate but necessary Windows XP machines.
744 soon: all WinEnt 1909 and WinPro 20H2. Please run Enterprise on campus; only DKU should be running Pro!
388 later: all 21H1, Ent and Pro, in mid Dec; all Win8.1 early Jan. Nobody should be running H1!
macOS
470 now: 324 Mojave, 74 High Sierra, 40 Sierra, 20 El Cap, 9 Yosemite and 3 Mavericks (Finally, no more cats! But that’s just since Jan…)
0 soon: With only one release per year there’s no worries in spring and summer, unless you remember that fall is coming…
1882 later: Catalina. Don’t wait, start now. Please.
Linux
106 now: RHEL 6 and Family make up 50%, Ubuntu 16.04 makes another 25%.
42 soon: Fedora 34 and Debian 9. Remember, all versions of Fedora have at most a year and a month of support. Upgrade early and often.
168 later: 99 Fedora 35 and 69 CentOS 8 (Consider migrating to Alma? Rocky? Stream?)