What is it?: Trueachievements (aka TA) is a site where Xbox 360 gamers can see how skilled they really are by seeing the TRUE value of their Achievements. Achievements are in-game awards for doing various things, some as easy as starting the game, others for doing harder tasks such as completing the game on the hardest difficulty setting and many other objectives, no two games are the same.
How does it work?: Gamerscore. Gamerscore (aka GS) is the value given to Achievements, the value can range from 0 to several hundred, depending on what type of game. A game bought from a retailer (these are larger titles such as Fallout, Call of Duty and Halo to name a few) or a smaller, cheaper game ( Feeding Frenzy, Minecraft, Castle Crashers) bought on the Marketplace, Xboxs store, and downloaded to the purchasers console.
TA then determines the Achievements TRUE value by comparing the number of people who have the game and those who have the achievement, this then gives you the TRUE value, which is handy as some Achievements are not given the Gamerscore they truly deserve.
The formula used to find the TA value is:
[Root(Total People with Game/Total with Achievement) x Achievement Gamerscore
For example, Dead Rising has an Achievement for surviving a zombie apocalypse for 7 in-game days, this translates to about 1 real life day, there is no saving, no pausing and your health constantly depletes, and after about 10 real minutes, you die, unless you find food. This can be a tough achievement, but its only worth 20 GS, like all the achievements in the game.
So using the formula, we can see the value of the Achievement. (numbers are rounded)
[Root(76,000/3,500) x 20 = 90
For those who like to see it in front of them.
76,000 / 3,500 = (roughly) 21, the Root of 21 is (roughly) 4.65 (this is the games ratio, for every 1 person that has it, this many do not), multiple that by the Achievements Gamerscore (20) and you get (roughly) 90.
The value changes daily, as many people may get the game or achievement.
What else is there?: Aside from state tracking (your overall game completion, your rank in your state, country, the world, custom leaderboards, your ratio (your GS vs your TA score) and rank across the whole site, there are also badges, these coincide with many things, number of posts on the forum, TA score, ratio and many other things.
You can also write or read solutions, these are short guides written to help others obtain Achievements, they can include tips, advice and even Youtube videos that show how something is done, make it good, as other members can vote on your solution, having it appear on the top, or at the bottom, hidden with the trash.
You can also join or create sessions to obtain Achievements that require multiple players for Co-op or versus games, this makes it easy to get those pain in the aAchievements.