i3status - status line generator (for dzen2 and xmobar)

i3status is a small program (less than 1500 SLOC) for generating a 
status bar for dzen2, xmobar, or similar programs.  It is designed 
to be very efficient by issuing a very small number of system calls, 
as one generally wants to update such a status line every second. 
This ensures that even under high load, your status bar is updated 
correctly.  Also, it saves a bit of energy by not hogging your CPU 
as much as spawning the corresponding amount of shell commands would.