Shout out to what I think is one of the best pieces of software, open source or otherwise (it is FOSS), I've used over the years: Zotero.
I first used it in college, almost two decades ago. It is still going strong, under active development with a huge community, and is available for just about any platform you're likely to use (no ARM linux binaries yet, but I can confirm it builds and runs on Debian ARM). iOS and Android versions available also.
If Obsidian is your thing, it works with Obsidian. It integrates with all major browsers, and the UI just keeps improving. It has been my combination document library, reading list, and citation generator for years.
They just released Version 8, so I thought it was a good time to give 'em a plug:
