Guide Best Apps for Android (FOSS)

Obsidian has a really good offering but if you want to stick to open source, another polished product I've seen is AnyType. It's cross-platform, local-first (like Obsidian), syncs using E2E encryption (P2P too!).

Unlike Obsidian, it's not a markdown editor though. More similar to Notion in that regard, it's block-based