Existing applications for Android? **Simply browse the [tag:android] tag here.**

As for writing an Android app yourself, I recommend the following Java library, which has been tested on the Android:

[StackWrap4J](http://stackapps.com/questions/818/stackwrap4j-java-wrapper)

Others can be found by browsing the [tag:android]+[tag:library] tags together, like so:

http://stackapps.com/questions/tagged/library+java