I first encountered this trend last Thanksgiving, while I was waiting for my return flight to San Francisco. A group of teenage girls had just lost a lacrosse tournament and were huddled around one player’s smartphone, making funny faces, and giggling. Curious, I wandered over and asked what all the fuss was about.

They introduced me to Snapchat, a mobile app so popular among the young adult demographic — or at least those with an iPhone or Android device — that Facebook  copied the idea outright late last year. It’s just one of several apps that seem hell-bent on keeping the mobile experience fleeting. Here are the three most important:

Snapchat

Founded by former Stanford students Evan Spiegel and Bobby Murphy as a class project in 2011, it’s now a tour-de-force with a huge user base some sources tell me number in the tens of millions. On first blush, the idea seems counterintuitive: Why bother sending photos to others that “self-destruct,” or vanish, in 10 seconds or less? It’s something I didn’t get, even as the gaggle of girls in the airport tried. “You haven’t heard of it?! It’s so you can like, send fun photos to each other!!” one of my new friends explained nonplussed. Indeed, Snapchat saves users the hassle of going back and deleting those photos off your phone, but it also serves as the antithesis to apps like Instagram. If Instagram is all about preserving and enhancing those amateur digital snapshots, Snapchat is the opposite: it encourages users to be more spontaneous and silly — sans Amaro photo filter — with users comforted by the thought their photos won’t be saved or shared.

Poke

Early Facebook users will remember the original “poke” feature: that ability to virtually nudge other users. When Facebook was a college-only social network, it was a flirty gesture; these days, it just seems antiquated and creepy. It’s also now the name of a Snapchat clone. Like Snapchat, Poke-rs may nudge each other, and send photos and messages that disappear after 1-10 seconds. As I pointed out last month, Facebook’s crime here isn’t just that it ripped off another product, but that it did it 
badly
. Though Poke hit No. 1 in Apple’s  App Store on day one, it’s doesn’t even place in the top 100 free apps on iTunes today. (Snapchat, meanwhile, still hovers at No. 27.)

Vine

Vine’s use case feels very much like Twitter’s artificial constraints around 140 characters, which shouldn’t come as a surprise since the startup is owned by the social network. Basically, users cobble together six-seconds-worth of video shot from their smartphones. “It’s going to force people to be creative and foster this new art form of ‘how can I tell this story in six seconds?'” Twitter CEO Dick Costolo told The Wall Street Journal this week. Those around Twitter are doing their best to get the word out about the app. (To wit, Twitter creator Jack Dorsey posted a video montage of adorable baby photos.) Whether or not it takes off is anyone’s guess, but Vine is undeniably easy to use. Take and edit six seconds of video? That’s pretty much something anyone can do.