Good catch, I didn’t realize that with AnyType. That makes my first recommendation to OP just SilverBullet, then. Source available is better than nothing, like with Obsidian, but OP specifically asked for FOSS repos. It looks like their peer to peer sync server is MIT licensed, but their client (and client library) code is licensed under the “Any Source Available License 1.0,” which restricts use other than for “personal, academic, scientific, or research and development use, or evaluating the Software, but does not include uses where the Software facilitates any transaction of economic value.”
I ruled out Logseq’s sync service due to it being both paid ($60/year minimum) and not FOSS, both things OP asked for. For my purposes, since it’s not FOSS and not able to be self hosted, it’s not a good option. But it makes sense to use the same file syncing solution that’s already in use, whether that’s FolderSync (or some equivalent tool) set up to sync to my server, Syncthing (though I just realized its Android client is no longer being developed as of December 2024), or even Cryptomator + some cloud storage service.
Learn, understand, challenge, repeat.
Learn as much as you can about all sorts of topics, even if you don’t have specific plans for those topics
Learn enough that you don’t just know the facts, but that you actually understand why things are the way they are. You should be able to predict things you haven’t yet learned if you understand the concepts. If you don’t understand something yet, keep learning.
Learn your fundamentals: language skills, math, logic, statistics, the science of research, history, politics, basic psychology, and the physics of whatever realm you’re operating in (meaning that in today’s day and age, you should learn about both real-world physics and about how information flows on the Internet).
A lot of people don’t know how to teach themselves, so it’s probably important to point out that learning to do so effectively is a big part of thinking for yourself. Learning how information is presented, as well as what’s often left unsaid, is important. Learn how to read graphs and charts and statistics. Improve your information literacy: Learn how to find credible sources, how to judge the credibility of a source, and what “credible” actually means. It doesn’t mean infallible.
As a general rule, don’t accept a fact until you have multiple credible confirmations of it. That might not be possible, but when information comes from untrustworthy sources, remember that. Learn the difference between something that you’ve learned and accepted and something that you’ve just heard on social media a few dozen times. This is easier when you have an understanding of what you’re learning. True things fit in better with other true things.
Don’t assume things are false just because the source isn’t credible, either. Just do extra research to verify. Do your own experiments to confirm, if possible.
Sometimes you’ll realize something you’ve accepted might be wrong, possibly because it conflicts with something else that you learned. When facts don’t add up, challenge them. You’re not infallible. Replacing a fact you accepted long ago isn’t a failure; it’s a victory. Many people are incapable of doing so.
Learn to distinguish between facts, inferences, theories, and opinions. (Note that established, accepted scientific theories often fall into the “fact” category.) Facts are verifiable. Inferences are based on facts; they’re evidence-based conclusions that can help to build theories. Theories are explanations, and they can be disproven but haven’t been proven (else they would be facts). Information presented as facts can be false. Theories and inferences can be poorly formed, even if the facts are sound (and especially when they are not). “Opinion” is a word people use to defend flawed theories. If the opinion isn’t a preference, there’s a good chance it isn’t an opinion at all and is just intentional misinformation. “You can’t argue with my opinion” isn’t applicable when the “opinion” is provably false - then it’s just a failed fact, inference, or theory. And even when it is an opinion, it can still be criticized.
Learn about logical fallacies. Even if you don’t call out the person using them, try to notice them in the wild, both by people you agree with and people you disagree with. But especially by people you agree with. Learn how to notice other ways people are misled.