Unless they’ve open-sourced it in the last year or so, Obsidian isn’t open source. That being said, it does have big vibes of open source. Like, there’s more to open source than simply the source code being available — it’s also about the general ethos of openness. When I was using Obsidian, I felt reassured that my notes were my own, and they would still function mostly the same if Obsidian went under. It’s a big part of why I switched to it from Notion