If you are working on your own application and would like to try out the Multiapp system with someone else's Application, you currently you have to run through a series of steps to add dependencies to the Makefile and register the other application explicitly.
This is no longer the case. MOOSE Now supports the ability to dynamically load other applications that may not be linked to your application in any way.
For this example let's assume your application is called "Tortoise" and you want to run "Hare" as a MultiApp. You might start with a block that looks like this in your input file:
[MultiApps] [./hare_app] type = TransientMultiApp app_type = HareApp execute_on = timestep positions = '0.0 0.0 0.0 0.5 0.5 0.0' input_files = 'hare_input.i' [../] 
Finally, you just need to tell MOOSE where to find this application:
library_pathto point to the folder containing the dynamic library
'../../../lib'. Using a relative path means this will work on someone else's system however MOOSE does support either relative or absolute paths.