I use Sheets and Docs extensively for idea tracking and project kickoff. Docs for a scrachpad of ideas, lists, links. When I start working on something, it gets its own Sheet with a backlog, estimates, progress columns. Once it is published it will likely use GitHub issues or Trello or something a bit more robust. I use Slides to make mini pitch decks and keep all the related files in the same folder on Drive. Next to the main list in Docs.

I am also working on an idea management platform, because I like Sheets but it is also a limiting experience. I'm making automated question-answer with TTS and speech recognition, and hoping to make automatic pitch deck starter kits from question-answer sessions in app. Maybe it'll be a product some day.