My friend Bill swore by his paper system, comprising wirebound pocket notebooks in four colors, one for each season. He bought a case, and never used all of them.
Years ago, I used Lotus Agenda to keep track of everything. I loved it, because you could just type something like "Meet Jerry for lunch on the second Tuesday of next month to discuss Project X, and it parsed the text and linked it to your calendar, your projects, your friends, etc. It's gone obsolete, and never really been replaced.
Since then, I've tried Excel, several times. It can do math on dates, and sort stuff, but it requires a lot of manual screwing around to stay organized, and just flat can't do things that Agenda did automatically.
More recently, I've just maintained simple chron files for each project, using Notepad. Hit <F5> to get a time stamp, then type what happened, or who said what, etc. Leave out opinion and supposition, and the files stay fairly small. Put 'em on a thumbdrive and carry it in your pocket.
Mike Halloran
Pembroke Pines, FL, USA