Notion has a very flexible data model. We use it mainly for documents, but it also can contain databases, which can be viewed as kanban boards, timelines, etc.

https://www.notion.com/blog/data-model-behind-notion

It's really nice to have one place to go for all kinds of content, but that content can link within itself, @mention other pieces of content, etc.

It can (and does) turn into a huge mess if you let it, of course. But that's down to team culture.