Whether saving for a big trip or to pay off a student loan, a number of apps are designed to help you save money in brand new ways – just a few bucks at a time. Here are three of the best personal finance apps to help you do just that. Qapital puts a unique spin on saving. It lets users set up so-called rules – for example, buy a specialty coffee drink and transfer $5 to your FDIC-insured account. The idea is that it will add up and you can withdraw from your savings with the push of a button. The app is free for iOS and Android. Acorns allows…