There is a preview of the upcoming Leadwerks Game Engine 4 available on Steam today.
From the announcement:
We completely rethought how large-scale scene management should work to bring you a one-of-a-kind vegetation system for handling massive amounts of foliage. Instead of storing each instance in memory, our new system uses a distribution algorithm to dynamically calculate all relevant instances each frame for rendering and physics. This allows enormous densely packed scenes with minimal overhead. The results are blazingly fast, efficient, and easy to use. In fact, the new system is so advanced it's featured in the upcoming book Game Engine Gems 3. Other features include autocomplete in the built-in script editor and integration with Steam Leaderboards.
To help you make the most of the new vegetation system, we're also introducing the Nature Model Pack DLC. This includes trees, plants, grass, and rocks, to make a variety of outdoors settings with.
Leadwerks Game Engine 4 is a free update and allows publishing of games for the PC and Steam Machines.
The timing is good as right now Leadwerks is 80% off on Steam.