Halo Waypoint has recently appeared on the 'My Community' area of the Xbox Dashboard for some people in the Preview Program.
The 'game' is a 130MB download and will appear on your game library and gamercard as a recently played title. The big pull here is that alongside news, the application will also reward you with Halo-based Avatar Awards depending on how many achievements you have across all three Halo Xbox 360 games (Halo 3, Wars and ODST).
You'll get a Waypoint Monitor prop just for loading the application and then a whole load more if you're a die hard Halo fan. The full achievements in all three games will unlock everything, or you can see the specific achievement you will need to unlock the next award.
It's certainly something that will make you consider picking up one of the Halo games you may have missed some achievements on.