When you are developing Visual Studio plugins, your project is usually configured to launch a special instance of Visual Studio under the Visual Studio debugger (excellent example of dogfooding), this special instance is called experimental HIVE.
Figure 1: Configuration of a standard VSIX project to test your addin
As you can see the project is configured to start Visual Studio as external program to be debugged and it is started with the option /rootsuffix Exp to start in Experimental Hive. This permits you to test your plugin in a configuration of Visual Studio that is isolated from your standard instance. As an example, you might develop a plugin that makes Visual Studio unstable and you cannot open Visual Studio due to this addin.
If you want to remove or look at the current configuration of experimental hive you can go to this folder:
You should see all configuration folders for the various editions of Visual Studio. Those that end with Exp are related to experimental hive.
Figure 2: Folders related to experimental hive.
You can now enter an experimental hive folder and in the extensions folder you should see all of your plugins that are under development. Now you can remove them if you want to restore everything to the original value.