I get the sense that a LOT of their early users switched to open source alternatives... primarily Logseq and Obsidian. Logseq is now my daily driver for "Personal Knowledge Management" and I really love the forward and backward linking capabilities. But it is a pain in the butt to use on mobile and to get syncing to work well.
Discussion
never heard of Logseq, and didn't realize Obsidian was open source. will check em out
Sorry my bad... after checking it looks like Obsidian is *not* open source. However Logseq most definitely is. Another open source project that I've had my eye on and you may want to check out is SilverBullet: https://silverbullet.md/ . I really like the server-first PWA design, but I've got so much momentum with Logseq that I haven't been able to do a proper evaluation yet.