The Common Lisp HyperSpec is a great reference for people who write Common Lisp implementations, but it is not (and it is not meant to be) a complete language reference manual.
There are also several good books for learning Common Lisp, but these books are necessarily limited in scope.
The purpose of this project is to write a complete language reference manual. It differs from the Common Lisp HyperSpec in the following ways:
It will contain many more examples, and these examples can be more realistic than the short examples in the HyperSpec.
For each operator, it will state explicitly what conditions will be signaled and what situations represent undefined behavior. The HyperSpec leaves most of this information implicit.
It will mention how different implementations define behavior that is undefined by the HyperSpec, and it will explain the reasons for the behavior in those implementations.
It differs from existing books in the following ways:
It will be a complete language reference, so necessarily much bigger than a typical book.
It will present the material so that it is easy to find some particular functionality, given a particular subject. It is not meant to be read sequentially.
This project has been started. It is currently located in a GitHub repository.