Perhaps the best way to explain Facebook's newest app is with bananas. One day, the fruits went from being plentiful snacks in Facebook's cafeterias and break rooms to the surprise stars of a crowd-sourced video made by its employees. People stepped away from their desks to capture short videos of bananas (or to be specific: "Mr. Banana") living life around the office like a human would. They'd walk down hallways holding the banana as if in first-person, or prop it up on desks and furniture. Anyone could get in on the phenomenon, collectively creating a saga that's silly but also fun. And the company hopes it will be compelling enough to lure people away from places like Snapchat and Vine.

All this was made possible with Riff, the latest project to come out of Facebook's Creative Labs, the same group that's come up with Paper, Rooms, Facebook Groups, and others. The idea is to let people record up to 20 seconds of video and share it with their friends, who can then tack on their own recordings immediately afterwards. You can post simple one-off videos, or create the beginning of something that takes on a life of its own — like the exploits of anthropomorphic bananas, or a night of karaoke, or reenacting the Budweiser "wassup" ads — all things that have happened while Riff was being tested.

The app, which is available on both iOS and Android today, originated not from fruit, but from last year's ALS Ice Bucket Challenge. People began posting videos of themselves upturning buckets of ice water on their heads in the name of charity, and Facebook noticed that people were suddenly using its service in a very different way than they normally would.

"My friends typically mostly post photos to Facebook, and text, and links, but I rarely see them post videos, and overnight every single person posted about the same thing, and they were all videos," says Josh Miller, the product manager of Facebook's Creative Labs and creator of link-sharing service Branch, which Facebook acquired last year. (Miller also led the development of Rooms.) "We loved how for the first time it felt like you were making something with your friends, not just sharing at them."

The ice bucket challenge led to a huge volume of videos, but no real way for people to see how they were connected. After all, under the rules of the ice bucket challenge, you could challenge people you knew to either donate or douse themselves. In theory, the videos should have been highly social. But they were all basically siloed off from one another.

By comparison, Riff videos have been designed as an evolving mix of clips that revolve around a topic. You can post something in the morning, and there could be a dozen or more additions to it during the course of a day, like a Facebook chat thread. Unlike normal Facebook comments, additions to Riff are designed to go viral. When you post a Riff for the first time, you tag it with a topic — be it one you've designed, or one that's trending, a la Vine. Your friends get a notification once you post, and when someone else jumps on, all their friends will see it, too. "It can get big pretty quickly," Miller says, while noting that the company hasn't really been able to see how large these threads can get since it was only tested internally. "The goal is to grow these things as much as possible and to get as many views and as many clips, but we don't really know — we've only been testing it with this small group of employees." Even so, a simple Riff thread of Facebook employees filming themselves covering their mouths with their hands topped 1,500 contributions.

That length issue is also why there are safeguards and tools to let you skip ahead. One is the 20-second limit, which Miller says is somewhat arbitrary and could ultimately change, but for now is designed to keep people from creating long, terrible videos. The other is a fast-forward button that lets you jump to the next Riff in the entry. Snapchat has something similar with its stories feature, which is absolutely necessary here considering each Riff clip can be twice as long. Offensive videos can also be flagged independently of the larger threads they're in, and Riff creators can selectively delete follow-on videos they deem offensive.

Miller is careful not to make any claims that this has been designed to directly take on the likes of Vine, Snapchat, or any other tools that let people share snippets of video, though there are obvious comparisons to be made to both. Snapchat's popular Our Stories feature in particular looks like a clear inspiration for Riff, with its crowdsourced collection of photos and videos tied to popular events around the world. But Miller notes some differences in the format. For instance, unlike Snapchat stories, which are compiled by Snapchat's editors, Riffs are created and organized by users, and have more sharing options.

"I love those Snapchat public stories, but for me those are a little more editorial in terms of like ‘I'm not at that event, and it feels like I'm there now,'" Miller says, adding that the curation Facebook's team plans to do is more of an entertaining nudge. "We don't know what a Riff is going to be good for, and our hunch is that we're going to learn from the best ones in the community. So the whole idea of featuring [Riffs] was not to have an editorial experience, but to say ‘hey ever thought you could do something like this with a banana?'"

Riff is a standalone app, but it will also spill out onto Facebook itself. You can choose to post a Riff to your Facebook profile for friends to see, and any additions made to it later will be added retroactively. That turns the videos into living, breathing things that people might come back to again and again, unlike any other video you'll find hosted on Facebook. And since there are no text comments in the Riff app, it also means Facebook is where all the discussion might take place, which could end up being a disjointed experience: strangers can add to a video you started, but won't be able to read the comments about it on your profile.

Details like that, and whether Riffs can eventually be embedded outside of Facebook, are still being considered, Miller says. That's how Facebook's Creative Labs group works. Recent apps like Rooms and Slingshot are the digital equivalent of throwing things at the wall and seeing what sticks. (And very little has stuck, at least to judge from the apps' rankings on the iOS or Android charts.) They're also slightly different takes on experiences people are having on already existing, popular platforms — something that's not necessarily a bad thing, Miller argues.

"Most of this stuff isn't going to be good, but it's going to make you laugh," Miller says. "If YouTube is the best karaoke on the internet — the child from Sweden who just can sing Beyoncé better than Beyoncé — Riff is supposed to be you and your friends laughing because you cannot sing Beyoncé and that's hilarious, not that the karaoke is a good karaoke song."