Frequent Flyer Travel Rewards is a free app that provides you with the option to earn and save up points for various rewards. These rewards can include making future flights free, or a variety of other options subject to what the app developer, Placed, can provide. Unfortunately, there are a few limitations: not every airline is available, such as United Airlines in the US and many (or all) airlines elsewhere, but the app is still worth a look for frequent flyers.