Free

Because OS X doesn’t have a free command

$ free
Usage:
  free [options]
       --watch, -w:   watch command
          --gb, -g:   view in GBs
          --mb, -m:   view in MBs
  --show-units, -s:   show unit size
     --version, -v:   Print version and exit
        --help, -h:   Show this message