Ecosia

Ecosia
Actually a search engine, Ecosia allows you to conduct your web searches while at the same time planting trees. At least 80 per cent of Ecosia's search ad revenue is donated to tree planting projects around the world (the organisation says it takes around 45 searches on average to plant a tree). At the time of writing, more than 32 million trees have been planted thanks to use of the search engine. The app is available for both Apple and Android devices.

Save the Trees!
Save the Trees! aims to promote awareness of the fact that some 2,000 trees disappear from the Amazon every minute through a simple game. Players have to try and save as many trees as they can from fire or being chopped down in a single minute by double-tapping trees on the screen as they catch fire or fall prey to a chainsaw. They're then informed of their score and pointed toward three NGOs to support which are helping address the issue. Addictive. Free for iOS.