Beaver seems to be open source, although I cannot find any link to the code nor license (although the "Terms" page mentions MIT: https://www.beavernotes.com/Terms.html)
Obsidian isn't open source. But, it stores your files are normal markdown files (cannot see if Beaver does the same) so it's easy to import/export if needed, and also have a huge number of plugins for basically anything out there.
Obsidian is also pretty established (read: "old") at this point so the ecosystem is already big, stability is good and it's mature enough to be used professionally. Probably Beaver doesn't come close to that (yet).
Obsidian isn't open source. But, it stores your files are normal markdown files (cannot see if Beaver does the same) so it's easy to import/export if needed, and also have a huge number of plugins for basically anything out there.
Obsidian is also pretty established (read: "old") at this point so the ecosystem is already big, stability is good and it's mature enough to be used professionally. Probably Beaver doesn't come close to that (yet).