Wren - Offset your carbon footprint by saving rainforests
Carbon Visualiser - See your CO2 in burgers, basketballs, pufferfish and more
EcoCart.io - Free e-commerce plugin for merchants to offer carbon neutral orders to their customers.
Klima - Go carbon neutral
Website Carbon Calculator - Find out the how much CO2 your website emits
Treeapp - Plant a tree for free, every day, in less than a minute