App Mahal is a social app to help users discover new apps that might interest them. As a user, you can follow other users, find out what apps they have installed, and help you find useful apps.
Some users might actually see this app as a violation of their privacy in some way. In fact, many people might not want other people knowing what apps they have installed, in which case they shouldn't use App Mahal. That said, maybe they should ask themselves what's more invasive: people knowing that you use eBay and Facebook ... or people seeing what you have for breakfast every day on Instagram.
That said, App Mahal works like any other social app: you can follow other users, and at the same time, be followed. This feature gives you an idea of what apps you might like or dislike.
App Mahal is an pretty interesting tool for finding other applications. As with other social apps, it's much more useful if you know a lot of other people who use it.