A bunch of Marathon players took 54 of their favorite small maps, edited them a bit to their liking (more ammo, lower ledges in some cases, etc.), and stuffed them into a single Map file, to make net play easier. Unfortunately, the documentation is a bit sparse... (hard to tell which map comes from where, or what was done to it). If you're looking for a large collection of maps that someone else has already said is above average, download this.