Pokémon Box is a game that allows players that own copies of Pokémon Ruby and Sapphire, and eventually perhaps Pokémon Fire Red and Leaf Green, to store Pokémon onto a Gamecube memory card. However unconfirmed, it is said that players will be able to store up to 1,500 Pokémon onto a memory card.
The only other known feature for Pokémon Box is being able to play the Pokémon Ruby and Sapphire games on the television. This is a feature confirmed on http://www.pokemon.com.