They describe it as:
Duck Marines is a cross-platform free software PC remake of Sonic Team’s ChuChu Rocket.
Duck Marines attempts to recreate the magic from the local multiplayer of ChuChu Rocket while adding new elements like mini games, a level editor, colorful pixel art and more.
But see for yourself:
For those not familiar with the original on the Dreamcast here is a small description of the gameplay:
The goal of the game is to get as many ducks into the submarine of your color. Gray ducks give you one point, gold ducks give multiple points and pink ducks will trigger an event or mini game.
Guide the ducks towards your submarine by placing arrows on the ground. When walking over an arrow ducks will instead walk in the direction the arrow is pointing.
Beware of the blue predators. Predators love to eat ducks and will kill a large number of your ducks if they reach your submarine. Try instead to guide the predators to the other players’ submarines using your arrows.