It's a ripe space. I'm using notion mostly right now, but I've also used:

-Coda.io (big, more scriptable player)

-Hypernote (super new player, but with a cool new take on inter-note relationships)

-Tiddlywiki (super customizable, really fast -- but also has a fair amount of footguns)

-Airtable (only played with it a few times but it's usually mentioned in the same breath as notion, I notice)

Hopefully someday we'll achieve Alan Kay's dream :)