MULTIPLE-VALUE. There are built-in variants for some standard operators; it's easy to create your own variants for other operators. The multiple-value mapping operators are especially useful.
The currently supported built-in multiple-value variants are:
(progn prog1 and or cond when unless case ccase ecase typecase ctypecase etypecase mapcar mapcan maplist mapcon)
Here are some examples of multiple-value mapping:
multiple-value-variants is in Quicklisp: