There isn't much in the way of game specific frameworks/engines. What does exist is largely immature though can help provide a higher level of abstraction for rendering:
- Sgine - http://www.sgine.org - This one has been undergoing a rewrite for a long period of time, I woulnd't count on this one for anything practical anytime soon. I looked at this early on in creating my game, and while it looked extremely productive for tiny projects, I decided not to use it after finding too many core problems in my mind to justify it's use in anything substantial.
- Simplex3D - http://code.google.com/p/simplex3d - Provides math, data binding and rendering libraries, I haven't used this one, but it looks solid for what it provides.
- Scage - https://github.com/dunnololda/scage - 2D only, I have little familiarity with this project, it seems tailored to small projects, the network api looks neat though.
I've built an engine directly on top of LWJGL over the past year. In retrospect it seems to have been a good idea. I honestly can't imagine using anything but Scala at this point (though except maybe Rust one day in the far future). I simply couldn't stand to use something as unproductive as Java or C++ again.
Not that it's a great measure of size, but my game including the engine/framework is approx 440 scala classes.
A side note: The game libraries suffer from similar problems to Scala libraries as a whole, especially in their (and in some way Scala's) relative immaturity, they're all written in their own interpretation of how Scala code should be written (something which is very diverse amongst scala libraries).