A file named TODO where I list modules/components/ideas, bugs and nice-to-haves (future version features that 99% of the time are not implemented). I tried PM tools but this trade is not linear nor predictable: I sometimes get stuck for a couple of days designing something or refactoring code, sometimes I just burnout and it takes a few days of limbo to get back on track. This trade is more like an art and constantly missing deadlines stresses me so I now try to just sit down, enjoy and finish as soon as possible. And judging for the number of SW projects that go over-budget and/or over-schedule I guess I am not alone here. I give my clients guesstimates and since I do periodic deliveries they feel we are moving forward so they are not so picky with PM deadlines anyway.