As anyone who has tried to build an app knows, creating something that not only engages users, but hooks them — getting them coming back multiple times, day after day — is no simple task. When one of these apps appear, ease of use and addictive features mean they take off like wildfire, leaving apps that struggle to acquire users to wallow in their inadequacy.

One of the best recent examples of an app that is neck-deep in the secret sauce is Tinder, an online dating app (iOS, Android). Less than a year after its launch, Tinder is the fastest growing free dating app in the US with more than 2 million daily matches, global momentum, and a spot in the Top 25 social networking apps. Tinder’s engagement statistics are the numbers other apps gaze up at in the sky: the average user logs in eleven times per day and spends seven minutes on the app each time.

But what makes Tinder so great? Ryan Hoover at Pando Daily explains that there are four elements that set it apart. Here’s one:

Simplicity: Tinder is so easy it is silly.  Users sign in through facebook, set the gender, age range, and location radius of their prospective match and they’re presented with what looks like an endless stack of photos to either swipe left (“Nope”) or swipe right (“Liked”), much like the old Hot-or-Not.  Only when both people swipe right is a match made.  It requires less than two minutes to set up and there are no contrived profiles, no complex rating systems, and no contact from people who aren’t interesting to the other person. The key here is that it requires very little mental energy — just a simple yes or no — meaning that people are likely to use it more often; something that appears to be working.  It’s also notable that the app is native to mobile and therefore easy to use anywhere and with friends, as opposed to at home alone like web-based services.

Although particular to dating, one of the features that makes Tinder successful is “Double Opt-in Dating” — both parties have to consent to the match before it is made. In traditional online dating, there is a serious mismatch where women are inundated with incoming requests and men get low response rates, causing dissatisfaction for each. Tinder solves this issue with simple consent. For even the most jaded dater, the app has some serious fireworks (relationship sparks still up to you).