Hi, I love Obsidian. It's part of my daily routine since a year or so, and I use it to store all my work and personal notes for the future. The main reason I use it is because of its note storage method. Instead of relying on a database, it utilizes plain text files written in Markdown, as most of you already know.
However, I have a strange feeling about it not being open source. The recent events with Reddit have only increased this discomfort. My notes are in plain Markdown, so I have the assurance that no one can forbid me from accessing them. I also take precautions by creating multiple backups, which provides additional security against virtual loss if I handle things correctly (which I do).
That being said, I would love to have alternatives like Joplin or LogSeq that adhere to the same philosophy of work as Obsidian.
Joplin is not suitable for me due to its reliance on database storage. I prefer to have total control over my notes.
On the other hand, LogSeq is more focused on serving as a diary rather than a personal knowledge manager, and it does not use pure markdown, wich will be a problem in the future when (not if) I'll need to migrate out of LogSeq.
A bit off topic considering your post is mainly about open sourcedness, but I use Logseq, migrated from org-roam on emacs...I love it. I have no reference to obsidian, although it's often discussed as an alternative. I don't know if obsidian has this feature, but in logseq you can issue queries to your database...it's amazing. It is journal based, though I haven't found that to be a barrier.