If SPARTAN Noble-6 and Chell had a baby, it would play games like this.
Halo: Reach had plenty of things to love, but one thing it didn't have was orange-and-blue portals that take you from Point A to Point B. Halo fan x7revorBlackx decided to do something about that.
Presumably using the level editor mod tools that shipped with Halo: Reach, he duct-taped together a level offering a rough approximation of what Halo might look like if the Covenant and UNSC forces started thinking with portals.
It's obviously not anywhere close to the real thing; the modder had to use the tools he was given, and Bungie didn't think to ship Reach with a portal gun. But a concussion rifle that places teleport markers when it blows up might just be the next best thing.