off the shelf - Everything2.com

Software, hardware or other products that can purchased through mainstream merchants, installed and used directly with little integration.

Most Microsoft products (Windows, Word and Visual C++) are off the shelf products.
FBI's Carnivore is not off the shelf (it's not for sale).
Several Linux distributions have recently become off the shelf, but the Linux kernel isn't.
desktops from Dell, Compaq and IBM are off the shelf.
Anything from apple is off the shelf.
DB2 from IBM and Oracle-8 from Oracle are not off the shelf because both of these RDBMS are designed to be customised after purchase by integrators.