GamePad Companion is described as 'Available exclusively on the Mac App Store. GamePad Companion 3.1 is a utility that makes it easy to configure your GamePads (controllers, joysticks, etc..) to play your favorite OSX games' and is an app in the Gaming Software category. There are three alternatives to GamePad Companion for Mac. The best alternative is USBOverdrive, which is free. Other great apps like GamePad Companion are Joystick Mapper (Paid) and Controllers (Paid).
The USB Overdrive is a device driver for Mac OS X that handles any USB mouse / trackball / joystick / gamepad / media keyboard and any Bluetooth mouse from any manufacturer and lets you configure them either globally or on a per-application, per-device basis.
Joystick Mapper is an application that allows you to configure your joysticks or gamepads to simulate keyboard keys/mouse movement/mouse click/mouse scroll, so you can control any app or game using them, even the ones without built-in support.