I'm looking for some kind of 2D graphics engine for Android. In my special case I only want to move some Sprites, play short sounds and perhaps play some simple animations.
I know, I could do all these things for my own but I'm interested in some other solution for personal reasons. So is there a good, slim, efficient and most important, open source engine out there one can use and contribute to?
AndEngine is a good option. It's free, it's open (source included) and it offers extensions for Box2D Physics, Live Wallpapers, Aug. Reality (Camera games) and allsorts of other stuff - LOADS of game in the market using it already (no royalties).
Cocos-2d is also a good option.
I mostly recommend Unity3d as it is simply awesome! It has a great documentation and many resources and tutorials. But for Android development, it is not free. Here is the price details and comparison of features.
Also check out the list of some game engines Here