I would say it's primarily a web application for note taking (there's some auxiliary capabilities around kanban boards, etc, but most people I know who use it, use it as a rich text editor).
I think where Notion differs from others, and where it has similarity to Org-Mode is it's ability to create 'blocks' with more dynamic behaviours (calendars, kanban blocks, tables) as well as how easy it is to create linkages between pages.
