Ask HN: How many concurrent projects do you have?
If just one at a time, how do you resist following the tangents which come up in any project?
The nice part about being disciplined in this manner, is that ideas that are nebulous in my mind are usually concrete by the time I get around to them. you would be surprised how much stuff gets worked out by just having a project floating around in your mind for a while.
Almost every time I go through my notes when starting a new project, I think "wow I am glad I let this one roll around in my head for a while" because the notes create a very clear and coherent idea, by the time I get around to working on it. And I can usually see by my first notes that if I would have dived right in, I would have spun my wheels reworking better ideas that just popped into my head at a later date.
Keep two text files on the desktop to sort them out, one small file (~200 lines) for concrete ideas and another large file for "future" or less defined thoughts.
Inside each are project code names and a list of notes underneath each one. That way it's easy to add and keep additional ideas to the project, but doesn't require me to log in to a project management app, commit to a repo, etc.
An unexpected benefit of keeping ideas from many different projects in single files is that an idea from one section often leads to an additional feature for another project.
Tangents don't usually come up... unless you're a paying customer or you've committed to paying me if I build a specific feature for you.