Bells and Whistles

advanced and extravagant attributes of a program

[By analogy with the toyboxes on theatre organs]. Features added to a program or system to make it more flavourful from a hacker's point of view, without necessarily adding to its utility for its primary function. Distinguished from chrome, which is intended to attract users. "Now that we've got the basic program working, let's go back and add some bells and whistles." No one seems to know what distinguishes a bell from a whistle.
[Jargon File]

the optional features built into a basic product to satisfy or impress as large as possible a number of buyers; the term "plain vanilla" is an equivalent slang term used to describe a product with only the most basic features.