I feel like I have a bit of an idea considering this is what Linus decided to work on as soon as he got a break from kernel development. But there are lots of industries/hobbies with crap software, and Linus chose scuba.
If he had been in college at the time he would have definitely decided to write an alternative to BlackBoard or Canvas.
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.
