Ask HN: How to Collaborate with a Cofounder Remotely?

I recently started working on a project with a technical cofounder, and most of the collaboration we do now is on email, but the threads get super clunky and long, and its impossible to recall what we had spoken about a certain topic weeks ago, and impossible to find the topic we discuss on the threads. I was thinking of using google docs for certain topics and take it from there but still not sure about that. Trello is more about to-do lists, which doesnt fit. I want to be able to collaborate with my cofounder and keep up to date for different topics and subtopics, say one is for fundraising, the other is for packaging the product and fulfillment, the other is for product requirements, the other is for branding, and etc. Then, when I need to look up what we've discussed about fundraising, I can just look it up and then update it there frictionless and super easy. Google docs seems like a good idea, but not good in practice. Any other tools?