I would say subsurface is to dive plan apps what calibre is to ebook management software. An all in one solution that works and imports from a variety of dive computers through libdc (a subsurface fork of libdivecomputer).

Alright, not git or linux, but not having to deal with crap spyware from the companies behind dive computers puts it on the same level of not having to install printer/scan drivers on linux. It kind of "just works", in the quirky way of some things that just work on the FLOSS world.

Moodle is the project you're looking for. It's actually really good, my university uses it