aremaC allows you to create real-time effects by stacking and nesting effects with arbitrary masks together! Real-time means you can see the result BEFORE you take the photo. You can even shoot videos with them.
You can create absolutely NEW EFFECTS with aremaC and upload them to the online library to share them with all other users.
This app usually retails for $0.99/£0.69 but at the time of writing in the US and UK App stores it is free. Click here to download.