Metacello is a package management system for Monticello that is consistent with the important features of Monticello:

Declarative modeling. A Metacello project has named versions consisting of lists of explicit Monticello package versions. Dependencies are explicitly expressed in terms of named versions of required projects. A required project is a reference to another Metacello project.
Distributed repositories. Metacello project metadata is represented as instance methods in a class therefore the Metacello project metadata is stored in a Monticello package. As a result, it is easy for distributed groups of developers to collaborate on ad hoc projects.
Optimistic development. With Monticello-based packages, concurrent updates to the project metadata can be easily managed. Parallel versio