Notion combines documents and relational databases in a single editor. That combination is why teams use it for wikis, project trackers, CRMs, content calendars and onboarding handbooks all in one workspace.
It is the strongest option on this site for internal knowledge that needs to stay findable, and the free personal tier is generous enough to evaluate it properly.
Flexibility cuts both ways: without conventions and an owner, a Notion workspace becomes a maze. It is also not a substitute for a dedicated project management tool once you need workload and portfolio reporting.