I am creating an application which will coordinate and organize a lot of standalone functions. For instance, the main application might be called ABC Company Operations, and within it might be Engineering Bills Of Material and Project Management Purchase Orders, among many others. I want to develop each of these tools as a standalone solution, then include them in the main application when I am done with them. For one thing this will allow me to distribute the main application with a fair number of tools complete, then issue an update when each new one is included, and for another thing having these functions in their own projects will cut down on the madness inside the solution explorer. 

Searching and reading have shown me how to include existing projects in a solution, but they are included as a reference - the files continue to reside in the standalone solution. This is not good because I wish to make any changes needed in the standalone, then replace the project in the main solution when those changes are done and also because I would prefer not to have all these solutions hanging around in a public place.

I tried just copying and pasting the project directory from the standalone solution into the main solution, but the solution explorer hasn't picked it up and there are somehow two listings of the standalone in the main Visual Studio screen where you select which solution you will work on. This seems like a bad road, so before I continue down it I would like to ask for any advice you folk may have.