I'd advise XBMC.
It scans local files (movies, episodes or music), 'scrapes' them for information (gets information about them from various websites), and displays them in a nice interface.
Examples of its default look:
There are multiple layouts to choose from, if the default doesn't satisfy you.
And if you want to give it a completely new look, there are a lot of skins that you can install to make it look more to your liking.
But that isn't all...
There are hundreds of apps and extensions to further customize XBMC. Think of a Youtube app, an app to watch live TV via internet, a µtorrent remote...
At the moment the website is temporarily down, but you can still download from here: http://mirrors.xbmc.org/releases/
(I'd advise downloading the latest version, xbmc-13.0-Gotham_rc1-x86_64.dmg - go to "osx" --> "x86_64")
It supports Mac OS X, Windows and Linux
Lastly, you can use it in windowed mode and fullscreen mode - use \ to switch between the two. (on Windows, I don't know about Mac...)