Technical Problem:

Have you created a new "Application Plugin" for MPS, which, however, can neither be seen within the development environment nor as part of the generated standalone application? 

So you have created a new "Plugin Solution" in your MPS project: 

Here an "Application Plugin Declaration" is then created within the "plugin" directory. 

The auto-generated file Standalone Plugin Descriptor exists in the same directory and has not been changed. The code to be executed for the "Application Plugin" is also created in the "init" area. Nevertheless, no functionality of the plugin can be observed? 

Troubleshooting:

Make sure that the configuration setting "Solution Kind" in the "Java" tab of your created solution for the "Application Plugin" does not have the value "None" but the value "Other".

With immediate effect, the "Application Plugin" should now be active after a "rebuild" of the solution, even within the development environment. If you want to run the plug-in code again for test purposes, simply right-click on the MPS solution and select the "Recompile Java Sources" option.