What tool makes you most productitive?
spudlyo: GNU ScreenMy top level screen session is a list of hosts I log into.  On each of those hosts, I also run screen (screen within screen) to give me virtual windows on that host.  As a UNIX admin this makes my life a lot more productive, as I'm often logged into 5-10 machines at once.  Instead of hunting around for the right window, I can jump to screens and/or subscreens by name, without taking my hands off of home row.  For me, one large multiplexed terminal window is best.  It also helps if your terminal program can go full screen (like iTerm) for maximum old-school terminal concentration.EmacsLearning how to edit text without taking your hands off home row (control key sequences) is invaluable.  This skill will help you in your editor, at the bash prompt, inside of any program you can run with rlwrap, and in OSX (or windows) edit widgets.  With a bit of work you can configure emacs keys in every GUI and non-GUI application you use.  For Windows users XKeymacs works well for this.  Linux users can configure GTK to support emacs style editing.  Having fast and universal controls for text editing makes me productive.straceWhy wonder why the a program is misbehaving?  See every system call it makes as it makes them, complete with arguments and return codes.  Even attach it to a running process to find out what it is doing in real time.  This tool has allowed me to diagnose and solve more thorny problems than any other in my arsenal.  For example, you're trying to figure out what arguments that gcc is using to invoke the linker in a Makefile, or which order that the linker looks for libraries, strace can tell you all of this, when you'd be otherwise scratching your head and guessing.Regular ExpressionsKnowing Regular expressions can make your life a lot easier.  In your editor they allow you do all kinds of advanced text manipulations, even some dumb refactoring.  Knowing them also allows you to do some great parsing in sed, perl, grep (ack is a better grep btw), whatever.  Once the regexp lightbulb has turned on your productivity can go way up.Server Side IMAP Email FilteringRegular expressions reminded me of this, but if you have all your email handling rules (filtering, organizing into folders etc) done on the IMAP server side, it frees up your email clients to be stupid.  They don't have to do any of that.  Your email inbox will look the same in Pine, Mutt, Mail.app, Outlook, your phone, whatever.  This is the promise of IMAP.  I use maildrop on my own IMAP server for this.