From GameBrew - a wiki dedicated to Video Game Homebrew.
AnkRace is a DS homebrew project started as a water effect demo that turned into a little game in which you bet on rubber ducks racing.
Bet on the duck you think is going to reach the finish line first. Some ducks are quicker than others and the starting position also matters.
Up/Down - Decrease/increase the size of the bet
Left/Right - Move through the menu selection of the duck
A - Choose duck
Start - Start game
Tested on R4DS R4 Wood (firmware 1.33).