I wonder if someone has study "fossilisation" in the FOSS world, there is a bunch a of key important tech that have very badly evolved and no one want to touch them anymore and those are often super critical and require a shitload of knowledge to learn correctly (and that totally sucks).
The ones I can think about (but I'm sure there more):
* mails (oh_god.jpg)
* mailing list
(I'm also tempted to say "anything related to netadmin" but that would be trolling 😋)