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You might want to take a look at AthensResearch (free, self-hosted RoamResearch clone).

Oh I have. Problem is Notion is most popular with the least technical people on our team. Migrating would be a hard sell.

This might be an interesting alternative: https://github.com/QingWei-Li/notea.

Open source Notion clone that you can host locally.

Looks awesome, but it relies on an S3 (or compatible) backend, which I personally find too much of a hassle.

Min.io[0] is pretty easy to set up, if you haven't heard of it, and is S3-compatible.