What apps work on iPhone 3?

The iphone 3G and 3GS, which run on iOS 4.2.1 as their maximum supported version, can use apps available on the App Store that are compatible with that version. Popular apps from that era include Facebook, Twitter, and simple games like Angry Birds. However, many modern apps require newer iOS versions, so functionality may be limited. Users should focus on lightweight, older versions of apps for optimal performance.