This app was mentioned in 3 comments, with an average of 4.00 upvotes
In case anyone is wondering like I was, the app lets you import your collection so that you have a database for your collection, which has benefits like:
a) organizing your collection/decks
b) knowing the current prices of your cards
c) contacting nearby people via instant messaging for trading
It looks like you can scan a card (with your camera), you can import cards in a txt/csv/dec file, and you can search cards individually and add them (?). You can chat with strangers/friends so you can trade with them too. Their app page has descriptions and pictures of all the features.
I enjoy the mage app https://play.google.com/store/apps/details?id=com.snapcardster.app