MameUI [formerly Mame32] is the GUI version of the M.ultiple A.rcade M.achine E.mulator, a program which seeks to document the internal hardware and code of all arcade games.
I don't have a wii u anymore to test it myself, but if homebrews are not visible on the wii u menu I think you can press L + R + minus to open the plugin menu, there should be an option called "homebrews on wii u menu" or something similar