I think the closest I've seen others do is blogging the development process, but that's usually a bit more polished and focused on the end result of the thought process on each decision, rather than - for lack of a better term - going on a journey with the author.
Does anyone else do this, in raw, unpolished form? If so, how do you store that (notes app, document, blog draft posts, etc.)?
The great challenge is to find a structure that suits you.
Knowledge management will become more and more important imho. For me, the crucial things are the learning from a process. You know how people write post mortems for system failures etc? That's kind of what I try to do, for important things. Sure, it's often just bullet points but the "What was the goal" -> "what did I do" -> "what did I learn" format really helps pulling it all together. Publishing and talking about it with others makes it even better for you and others.