This app was mentioned in 7 comments, with an average of 2.57 upvotes
It's like a multi but it's backed by a "program" that is interpreted by an application. I tested WhereYouGo, it's a little ugly but works!
Basically the program, called cartridge, has a serie of locations and reacts to you entering or exiting them. The program can prompt you with a description when you enter a phisical location, and you can interact with virtual objects or characters that the author envised, or you can be asked to check some real life detail such as the classic "count the number of letter in the sign".
The cartridge can give you tasks, trigger events, mantain data about your progress and your inventory, etc. As the "story" unfolds, new locations or object can be made available. It's basically like a graphic adventure (such as Monkey Island) in real life.
While i like the idea i think it's hard to come up with something that's both interesting and simple enought to avoid the user getting stuck at some points.
For Wherigo's, WhereYouGo for Android recently had an update so it should work with most newer phones. (2-3 years old). I dunno about iPhone though, sorry.
In android, when I click on a whereigo attachment in a gmail email, it now automatically opens the android app and saves / plays https://play.google.com/store/apps/details?id=menion.android.whereyougo&hl=en app.
If you're on Android, use the WhereYouGo app. Download the Pocket PC version of the cartridge form the whereigo website.
Android phone plus this app is the best combo.
Try the WhereYouGo app if you have an Android phone. I don't know the equivalent for iPhone.
You're looking for something like this: https://play.google.com/store/apps/details?id=menion.android.whereyougo
It takes a bit of work but you can program the cartridge yourself.