One laptop per child. The XO laptop has been through many changes since its conception (it's no longer the "$100 laptop" and the iconic hand crank has been replaced, for example), but the mission and vision behind it have stayed on course: "to provide children around the world with new opportunities to explore, experiment and express themselves." Through December 31st, you have the opportunity to participate in this endeavor by donating a laptop to a child and receiving one for a child in your life, too.
A donation of $399 ($200 of which is tax-deductible) will provide a laptop to a child who would otherwise not have access to such technology, nor access to the world through the internet. You'll also be sent a second laptop for your own child. A donation of $200 will simply send an XO laptop to a child in need somewhere in the world (this method of giving does not expire on 12/31).
It's not a coincidence that the XO is the color green either - it has been designed to be extremely energy efficient. Learn more about the laptop's features and specifications here. Read more about One Laptop Per Child (OLPC) here.