I ran my agency for 8 years, and we had a small clients, but worked on large complex projects.

I started with Google docs, then Confluence, then Notion - but I could never find a tool suitable (and opinionated) enough for capturing all this info.. as I really wanted to build a map of the system in docs, that was easy to reference when the next sprint comes up.

Userdoc has been designed to facilitate the initial collaboration with the client (user story mapping, personas, journeys etc), but also be a business asset, where requirement specs are iterated on, approved, and kept as long term documentation. As an initial test, we used Userdoc on a very large government project, and it significantly helped the whole team.