I once tried using a Hipster PDA to keep track of any ideas and such. Right now I'm trying out Google Keep to keep track of my errant ideas as I always have my smartphone by me anyhow.
My smartphone has quickly been overtaking my old-school note-booking ways. The thing is, I rarely flip through my "pages" of notes on my phone, but I often would on a real notebook. I just use the "notes" application that came standard on my phone. Is there something more out there that I'm not aware of?
I'm not sure. The big player in productivity apps is of course Evernote, though I haven't found I need as much functionality as they offer. Right now I'm just using it because I kept forgetting ideas for blog posts that I had. For stuff like software I try to keep what I'm doing documented and version controlled so I never have to look at my own code and think, "What was I try to/going to do here"