I just released the new release of VSLab codenamed R. Daneel. This release adds the package feature, an important element to build DSL and tools on top of VSLab. Packages are simply .NET assemblies with appropriate metadata used by VSLab to offer a dialog to manage them. Ok, ok you can code it, but it's handy to select which packages should be loaded, if at startup, and if you are lazy enough you can even ask for automatic namespace opening!
This is how package manager looks like:
You can load packages interactively or flag them for startup. You have two assembly caches (different from the GAC so you are not required to understand strong naming) for packages, one in the VSLab installation dir, and the other in the user profile. I managed to start the UAC dialog on Vista to have packages installed under program files.