Modularize-Hooks
This is a simple extension to Modularize that allows modules to define and trigger hooks, which other modules can hook on to. While such a system is very easy to create for your own projects, it's a good idea to have a standard form of doing it that doesn't interfere in any other way.

The project can be found on github including a fully documented symbol index and a getting started tutorial.
As of August 2014, Modularize-Hooks is available on Quicklisp.

Modularize-Hooks is licensed under the Artistic License 2.0.