You can make it - Open Source MMORPG Platform
Game engine supporting many 3D/2D formats and graphic effects
Example code for creating a 2D platform game in Java.
Mahasona engine is an open source game engine.
A generic 2D engine for any kind of game
A retro style video game engine for RPGs and adventure games.
A lightweight HTML5 Game Engine
UtiliGame is a light-weight game engine written in Java.