This is a demo of Mario Kart: Double Dash!! that can be found on GameCube Multi-Game interactive demo discs 13, 14 and 15. It's pretty obscure and not many people know about it. It also contains heaps of unused content (at least compared to the final version).
The Demo itself is pretty simple; you choose 2 characters from the starting roster, then complete a simple 3 lap race around Mario Circuit and then the demo resets itself.
The file itself is in .gcm format so it should work with Dolphin Emulator and most other GCN tools.