Apps are, quite literally, a dime a dozen. (OK, probably more realistically $12 a dozen at $0.99 a pop.) But while a steady stream of mobile apps are released every day, most notably for the iOS and Android platforms, there are a few that have really stood out over the past few months, gaining viral status. Here are 4 of the most-talked-about free apps introduced of late.

Microsoft’s Guess My Age How-old.net

Talk about going viral. Microsoft may or may not have known just how many people would jump on its How-old.net app (iOS, Windows) that it launched simply as a way to demonstrate its Face API at the Build conference in May using sample images, though there was a tool let you upload your own. It didn’t take long for Facebook feeds to be flooded with photo after photo with bright yellow bubbles above each person’s head indicating how old the face detection and recognition algorithms predicted they were. Feeding into our ego-driven culture, people were mesmerized at how the app would shed 20 years off their lives,add a few unwanted decades, or simply shoot out predictions that were so far off either way that they were hilariously ridiculous. Either way, it put our “me” culture in the spotlight. Not long after its release, folks began warning about the fine print, which eager participants didn’t realize indicated that if they uploaded a head shot, they were giving Microsoft permission to use their mugs in future advertisements. Interestingly, the app today has a “P.S.” under the upload photo button that says Microsoft will not keep your photo.

Who Deleted Me

As one of the most recent examples of apps that shot from obscurity to fame, Who Deleted Me promised to scan your Facebook Friends list and show which contacts have deleted you, which you’ve deleted, or tell you if someone just deactivated his account. While it could only provide data from the time you downloaded it onward, users couldn’t help but eat it up and satisfy their curiosities. Adding another level of creepy, the app could even tell you when a contact last logged on. By the way, speaking in past tense is no mistake: Facebook didn’t take too well to the app, and strong-armed the developer into shutting it down a mere week after it began making headlines. But the app was around for long enough to become a viral hit, and again, feed our ego-driven appetites.

Tinder

Everyone has at least heard of Tinder (iOS, Android,BlackBerry, Windows) though many admit (truthfully or not) that they have no idea what it is. Turning dating into a sport, it almost works like an amped up version of online dating, letting users essentially flip through profiles and photos of others, passing on ones they aren’t interested in, or liking if they want to chat more. The site says it’s a “fun way to connect with new and interesting people around you.” But pop culture has painted it in a much different way, essentially as a means of setting up an intimate rendezvous on the fly. The app has become so popular that the word Tinder, and the description of “swiping left” or “swiping right” has become part of common vernacular for many. With Websites like Ashley Madison just confirming a major data breach, chances are more people will flock to far simpler options like Tinder to fuel their, er, dating desires.

MyIdol

This app (iOS) became so popular that people were downloading and using it even though it was only available in Chinese. Luckily, even if you don’t know the language, the concept is simple enough that you can fake your way through the menus. What’s so great about the app? Again, feeding this generation’s narcissistic tendencies, you can snap a selfie or upload a photo of yourself, and it turns you into a eerily lifelike 3D avatar cartoon. Add outfits, hair, and accessories, then make your idol do everything from belt out a Britney Spears tune, to make heart symbols with your hands. Share the pics or videos with others, or just laugh hysterically at the cartoon version of yourself.