I have started a new project on CodePlex called 'GAC Manager'. This is a project that is in two parts, the first is a simple tool to allow users to manipulate their local global assembly cache, the second is an API that provides the core functionality.
Here's a screenshot of the tool in its current state:
An article on the project is available on the CodeProject at: http://www.codeproject.com/Articles/430568/A-GAC-Manager-Utility-and-API
The project itself is at: https://github.com/dwmkerr/gacmanager
As always, comments, feature requests and so on are welcome!