This is a model based on the My Little Pony: Friendship is Magic/Portal 2 crossover fanfiction "Better Living Through Science and Ponies," which takes place after Portal 2. In it, after being transported to Equestria and becoming a pony, Chell finds out that GLaDOS is kidnapping the citizens of Ponyville and using them as test subjects. Obviously human equipment wouldn't help them, so the evil AI modifies the portal gun to fit a pony's hoof. She also combines it with a long fall boot so the test subjects can safely land without having to worry about damaging the gun.
What's important, however, is what this model is for. I am a member of a currently small but hardworking team of creative bronies known as Thinking with Ponies. We are working on a mod for Portal 2 to allow you to play through this fanfiction and all of its Portal and pony goodness! We do not have all that much work done, but we are still relatively early in development, so we will continue working hard on it.
Note that this is by no means the final model. This is simply a rough work done by me. It still definitely needs some ironing-out. It serves its purpose for now, though.