Indeed. The closest I came to what I need was a proof-of-concept I did - printing source code to PDF and using Adobe Reader's annotation tools. Wasn't exactly convenient without a good ability to switch between multiple source files, but could be made to work. I'd love to have such browsing/annotation tool I could take with me to a park, to browse code and think about it while on a walk, without continuous distractions of the office / Internet connection.