Microsoft recently released Halo Waypoint to the Android Market, bringing an official multiplayer companion to the palm of your hand. The app has a surprising amount of awesome features, including live overhead views of multiplayer maps (with weapon, vehicle, and player locations), score information, and the ability to "stay in contact with your Halo friends on Xbox LIVE no matter where you are."
On top of all that, Halo Waypoint tracks your career and campaign progress and stats according to weapons and enemies, and enables users to invite friends to challenges from their mobile device.
The icing on the cake? Halo Waypoint is free from the Android Market. It's not available for all Android devices just yet (if you have a qHD display, for example, you're out of luck) but the developers promise wider compatibility in a "future update."
If you're a Halo player with a compatible device, head to the Market and give Halo Waypoint a try.