Find a popular app on iPhone and develop it on Android. Or vice-versa. Or develop a new, unique mobile app (that is more risky than implementing a proven conce

Find a popular app on iPhone and develop it on Android. Or vice-versa. Or develop a new, unique mobile app (that is more risky than implementing a proven concept on a new platform). However, be wary of tools like phonegap. Mobile market is very competitive so the quality of the implementation is a big factor in success if there are multiple implementations of the same idea. Pick one platform (either Android or iOS) and go native. Android, thanks to using Java, is easier to program natively than iOS. As a bonus, the market for both Android and iOS devs is hot and will grow in near future so as a bonus, you'll be able to convert your experience into well paying job (or contract work).