This slide in a recent playn presentation shows clearly the differentiation between playn Core API, and third party libs and engines. I wish to re-implement as little as possible, is there an obvious method to source these libs and engines that will combine with playn?
The playn-jbox2d.jar used in the showcase, I assume this a specific build of the java box 2d lib for playn? Will similar manual porting be required for other libraries or can e.g. Android libs be easily reused?
PlayN is a completely different API than Android, so you cannot use an Android game development library with PlayN. Higher level libraries are already being written for PlayN (for example, http://github.com/threerings/flashbang-playn), but since the platform is relatively new, not as many such libraries exist as for Android directly.