(this top was formerly title 'FPS Engine', I've since given the project a name and open sourced it on Github).
Github Repo: https://github.com/jrenner/gdx-proto/
GDX-Proto is a lightweight 3d engine for libgdx.
Some of its main features are:
1. fast collision detection using bullet physics library (but not simulating the world, for better performance and allowing manual collision resolution).
2. collision resolution in Java code, easily modified, or used as is.
2. full featured server/client networking with entity interpolation and client prediction (no prediction for projectiles yet). Local single-player play is also supported, of course.
3. simple entity system that handles velocity, position, rotation with easy to use API
4. support for Decals (billboard sprites) or 3d models
5. simple chat system over network
7. uses libgdx new 3D API
It's early days and the project is immature, but there is already a nice FPS demo jar that can be downloaded and run from the github repo bin directory.