It's SaaS only, so no locally stored data.

https://www.notion.so

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.

They have good SEO