The Midwestern Brotherhood power armor, called simply power armor in the game, is a suit of armor, used by the Brotherhood of Steel. The T-51b power armor is seen only in the intro. In the game itself, it is replaced by this horned armor. A more technologically sophisticated version, the Midwestern Brotherhood advanced power armor, also exists.
I would redo the sprite of the Power Armor to make it more retro. Not that there is anything technically wrong with the sprite, it's a great piece of art. It's just that it is a bit out of place in the Fallout Universe. But bear in mind that we had to design it over a year ago and Interplay approved everything we did. - Tony Oakden, producer of FOT (Freelancer interview)
Why does the Power armor look so different from previous models? - Different group of BOS, different technology. - Ed Orman (Freelancer news)