The Velocity Engine by Reflexive Studios

Icewind Dale 2 Lead Designer, J.E. Sawyer of Black Isle Studios describes Reflexive Studios' Velocity Engine used in Lionheart as the following:

It uses software anti-aliasing. This smooths the edges of sprites into the background, removing the pixelated edge that you often notice in Icewind Dale (look at a screenshot of a dark character standing in the snow for a good example of this). A lot of the press folk looking at the game thought it (Lionheart) was running at a much higher resolution than it actually was. (Ed: Because it looked extremely smooth.)

The graphic data files are .jpgs (JPEG) with an excellent compression:quality ratio. They take up very little space, which is often a big concern for 2D games.

The character models and animations are 3D. Animations traditionally take up a lot of storage space because you have to save off every frame to a separate 2D image and play it back like a flip-book. The character models in Lionheart are rendered in 3D, then put in the scene as a 2D image, so the main memory hit is in RAM.

You can run an "editor" version of the EXE which is fully functional, but also gives you level run-time access to the editor. This is really terrific. You can move around objects, swap out scripts, and change object properties while the level is running.

From what I can tell, it's almost entirely script-driven. There are drawbacks to this, but it makes the engine very flexible.

The engine is 2D, but gets around a lot of the traditional 2D problems.

* The engine has been used in at least three very different games: Zax, Ricochet, and Star Trek: Away Team. Whether you liked those games or not, they do show that the developers can easily modify the engine for a number of different roles.