cl-pcg is a permuted congruential generator implementation in pure
Common Lisp.
Permuted congruential generators are seedable, small, fast, fairly-hard-to-predict random number generators. They can be useful for things like games. They can also be advanced and rewound efficiently.
PCGs are not cryptographically secure. If you need that, look elsewhere.
cl-pcg can be installed with Quicklisp: (ql:quickload :cl-pcg)