So about that 2.5d template on a two-dimensional environment. How will it work?
You will be able to use a set of functions and rendering techniques to build your game with objects that have their physics based on three-dimensional points. Let me explain:

1 - Point rendering.

This system will select where to draw the origin for your character. It is the second most important part of this engine.
You can render the game however you want using mathematical expressions. However the default renderer will be ISOMETRIC. You'll be able to set the angle of viewing and things like that.
The good part is that the physics/position engine and the renderer are completely independent. That means that you can really render the way you want and even switch renderers when playing and the world won't be affected. Just the way the player sees it will..

Top down RPG Renderer:

x: px
y: py - pz

Isometric Renderer:

with a constant "a" storing the angle.
x: sen(a) * (px) - cos(a) * (py)
y: cos(a) * (px) + sen (a) * (py) - pz

2 - 3d Space Functions.

I will also include a small library with position-based functions that work with 3 coordinates, such as "distance", "isoverlapping".

DISTANCE
You will input 6 parameters for that function instead of two on the 2d one. It will return the distance between the points.
All the objects within a certain distance from a point are encoded on a sphere!

IsOVERLAPPING
You will give 12 parameters for this function (geez).
3 for the first's point.
3 for the second's point.
3 for the first's collision box (pxwidth, pywidth, pheight).
3 for the second's collision box.

And more to come.

3 - Particles on the 3d world. Also support animated particles.

4 - 3d Angle functions (to rotate characters acoordingly to the world.

More information