[subv3rsion]

I've been using Evernote to handle a lot of that. Between the web version of Evernote, apps for Android, iPhone, and iPad. It is always available. Not just for coding or IT either. I started using it for recipes as it is so ubiquitous.

[ISeemToBeAVerb]

I second Evernote. While I don't use it for this particular problem, I use it for TONS of other things. I can't even tell you how many apps this single app has replaced for me.

[stonk]

I third Evernote. I keep a single note for each largish task or smallish project and add points for each new thing I solve. It's great to come back to 6 months down the track...I remember doing this before, but how did I fix it then?