ArkhadosNet is free and open source UDP networking library that is based on jMonkeyEngine 3. ArkhadosNet is developed so that it fulfills the needs of Arkhados, which is very fast paced 3D online multiplayer action game.
ArkhadosNet is work in progress. It's not very stable yet.
ArkhadosNet uses the same license as jMonkeyEngine 3, which is 3-clause BSD license (aka "new BSD license").