In Stiktu, an augmented reality graffiti app, you scan objects around you, such as magazines, posters, or products, and then add text, stickers, and sketches to them. Later, when someone else scans the same product or item using Stiktu, they'll see your virtual graffiti. You can share your creations on Facebook and Twitter, and the app has its own like/friend system as well. Stiktu is currently available only in France, Germany, Greece, Ireland, Italy, the Netherlands, Portugal, Spain, and the UK.
Download for iPhone (free)