See the SICL project on GitHub.
We believe that having first-class global environments in a Lisp system is the key to making it the foundation of a Lisp operating system. By giving each user a private global environment, we can make it possible for individual users to customize the system without influencing the behavior of the system for other users. For instance, a user would be able to add a method to print-object or add a new class without those effects being visible to other users.