Some weeks ago another company was developing an web app for a common customer. This application should be integrated in MODx, but I didn’t make any indication about the way the should code it to make it compatible with modx ( it was no needed really ). One day, with work really advanced, we was talking about it and the only intruction I gave them was: make it as you want, but everything managed trought a controller ( example: web-app.html?action=open&id=2 ).
Once the work was done, I paste the code of the controller in a new snippet, uploaded the files, created databases.... and it was done! A complex web application was installed in a few steps, without any special indication to make the integration with the cms