One I butt heads with regularly -- still having to support IE 5.5 in 2018. See, a lot of free clinics, mental healthcare facilities, and so forth are ridiculously cash strapped because of clients with no insurance, no way to pay, and a mission to NOT turn away people in need of mental health care...
... and as such they're stuck with outdated hardware that was low-cost junk when new, like Geode and Samurai powered thin-clients running windows CE out of ROM.
You have to remember, IE6 didn't reach Windows CE/Mobile until 2008 when Mobile 6 came out; so until then almost EVERY embedded Windows CE device had IE5 as the ONLY browser choice. What, you missed the big 6 on 6 party? So did everyone else! Serious case of 'worse late than ever' in that IE 6 "finally" made it onto windows CE just in time for IE9 to come out for desktop. Then they wonder why are considered a joke in the mobile space.
The money doesn't exist for them to go out and replace everything with even cheap options like nettops, so it's cheaper to just have someone like myself keep their old in-house crapplets and web-facing stuff fully supported.
Though this is surprisingly NOT as hard as people make it out to be, if you just stick to semantic markup, conventional functionality, separation of presentation from content, and properly plan for graceful degradation. It will WORK, doesn't mean it will be pretty. They don't get some drop shadows or rounded corners, or some goofy bit of "gee ain't it neat" scripting, OH WELL!
You make it work, then you enhance it with the new stuff in a manner that if said "new stuff" fails, the page is still useful and usable to the user.
It's still a batshit requirement though, supporting twenty year old browser engines.