The Galaxy at War feature of the Mass Effect series launched with the third entry, Mass Effect 3, and is also tied into the Mass Effect Datapad app for iPhone and iPad, as well as the iOS game by Iron Monkey Studios, Mass Effect: Infiltrator.
Mass Effect 3
Mass Effect 3 is the series' first entry that contains a multiplayer aspect. The multiplayer is a horde-type cooperative mode in which up to four players must fight through 10 waves of enemies. Playing on a random map gives a boost to your Galactic Readiness rating throughout all theaters of war, whereas self-selecting a map will only give a boost, a much more substantial one to that particular theater. Each area can go all the way up 100% readiness, but each day the readiness rating decreases automatically. Playing the Galaxy at War multiplayer does require an online pass, which comes free with the purchase of a new game, or can be purchased through online services.
Whatever level of readiness the player achieves in Galaxy at War feeds into his or her Mass Effect 3 campaign. In Mass Effect 3 you must accumulate war assets which are represented by a number - total military strength. However, if the player only has a 50% Galactic Readiness rating, then only 50% of military assets will be effective in the final battle with the reapers. A certain level of effective military strength must be achieved to initiate the final mission, but this number also plays into the ending cinematic that players see after completing the game.
Mass Effect Datapad
Another way to boost the Galactic Readiness rating is through the Mass Effect Datapad, which is a free app available for iPhone and iPad. This app includes access to the in-game codex, the Mass Effect twitter feed, emails from you in-game squadmates, as well as the Galaxy at War game, which is somewhat similar to a Farmville type game. This game contains the same map as the Mass Effect 3 multiplayer and you can send fleets to one of three conflict areas in each theater. Each conflict area has an attached boost to that theaters readiness as well as credit which can be used to purchase upgrades, as well as a cool-down time. After taking time to purchase all the upgrades, this app can actually have a pretty substantial boost to the overall Galaxy at War rating. Since it is free it makes a great alternative for players that don't want to purchase an online pass or don't enjoy the Mass Effect 3 multiplayer.
Mass Effect: Infiltrator
Another way to boost the Galactic Readiness rating is through the iPhone and iPad game Mass Effect: Infiltrator. Although it costs $6.99 through iTunes, it is actually a legitimate game. Developed by Iron Monkey Studios, Infiltrator is very similar to the Dead Space game that they also developed. Infiltrator is a third person shooter and occasionally downed enemies will drop pieces of intel which can be uploaded to the Galaxy at War system. Each piece of intel is approximately 1% readiness to 1 theater of war.
In order to have benefits from the different games count towards Galactic Readiness in the Mass Effect 3 campaign, you must attach your gamertag or PSN account to an Origin account, and then sign in on that same Origin account in whichever one of the iOS games that you play.