I have some vague recollection of this feature existing, but it wasn't until this last week that I needed it again:
When working on a project with multiple executables within the same Solution, Visual Studio can Start all of them when you debug if setup for it.
Simply right-click the Solution and choose Properties. Choose Startup Projects from the left pane, then select the Multiple Startup Projects radio button.
For each project listed, you may choose to start it normally or without debugging. By using the Move Up and Move Down buttons, you may change the order in which the projects start!