Frontend typically refers to a GUI (graphical user interface) for a command line program (DOS/Unix) that doesn't have a GUI of it's own. There's been no reason to use a frontend for MAME for over a decade now.
There are, however, several different builds of MAME that may or may not have different GUIs than the official Windows build. I haven't did any investigating into the various forks for quite some time, but the version of MAME I currently use is MAMEUI64.
