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It’s .silverbullet.db in the root of your space folder. Note that because there’s no schemas in SB, SQLite is used as a fancy key-value store and many queries become somewhat (but not very) optimized table scans. In this SQLite file you’ll see a “kv” table that contains everything.
While I cannot give you an in depth comparison, I’m sure there’s a lot of overlap in functionality. Where I think things are heading in a relatively novel direction is with the recent improvements I’ve been making to templates. While long, this video gives a reasonable sense of what that can do and I’d say it’s early days: https://youtu.be/ZiM1RM0DCgo?si=qL795lyKNe9HwoxI
It’s perhaps a bit of a different beast, but you may give a quick look at https://silverbullet.md.