From About.com; Barbara Nefer

There are various types of "green" cat litters on the market, but a company called Boxiecat is taking things a step further with its home subscription service. The litter itself is environmentally friendly, since it's a biodegradable clumping variety, and its packing is designed to be as earth-friendly as possible. Users sign on for regularly delivery so they don't leave any carbon footprint picking it up themselves.

Even though it takes a truck to get the litter to customers' doors, it's delivered via the post office. Since postal employees already deliver to everyone six days a week anyway, there is no added waste. Boxiecat estimates that using this existing delivery channel saves 40,000 pounds of carbon dioxide emissions annually for every 1,000 subscribers.

Boxiecat on About.com