CUPS - Common Unix Printing System
CUPS provides a portable printing layer for Unix-based operating systems, and is a more-or-less standard printing system for Linux and MacOS-X. It uses IPP (Internet Printing Protocol) as a basis for managing print jobs and queues. The software is licensed under the GPL...
It is a drop-in replacement for BSD LPD that provides considerably more functionality. You can use either BSD flavoured printing commands (lpr, lpq, lprm, lpc) or the System V flavour (lp, lpstat, ...) It also provides a web-based configuration interface.