Viddy is so hot right now.
The video-sharing app for the iPhone has rocketed to more than 350,000 users in its first five weeks since launch--over 100,000 of them downloaded the app in the last couple days. That's a faster rate of growth than Twitter and Foursquare. "It's been wild," says CEO and cofounder Brett O'Brien. "We haven't spent a penny in advertising--we just turned it on."
Think of Viddy as the Instagram  of video. With Viddy, "Viddyographers" can snap short 15-second clips, apply one-click filters and effects, and share them with friends. "It's a simple way of making raw video look cool with iMovie-style production effects," O'Brien says. It's also becoming a new medium for connecting with friends and fans beyond a still image or 140-character message: Beside celebs like Sheen and Hilton, popular lifecaster iJustine  has hopped on the service, not to mention tons and tons of users looking to upload footage of--you guessed it--their cute pets. "We have something like 20,000 cute dog videos," laughs O'Brien.
So far, Viddy has raised $1.6 million from investors that include Battery Ventures and some early team members from YouTube. O'Brien sees big potential for the service, from sponsorships to branded production packs. "Looking back, you can imagine when Tron: Legacy came out, there might be a Tron-branded production pack that would easily transform video with cool neon effects and the Daft Punk soundtrack," he says. "We'll be working with movie studios, celebrities, and musicians to create unique production packs--it's kind of like the ringtone model." In addition to the free app, Viddy also plans to release a premium service--think Viddy Pro or Viddy HD--which would give users access to more production packs, better editing tools, and longer-length video.
To be sure, Viddy has faces some stiff competition. A slew of apps promise similar video-sharing capabilities, from SocialCam to Vlix. Flip Cam came before it, backed by millions of dollars in advertising, and failed to crack  the mainstream market enough for Cisco to keep it alive. And there's always the looming shadow of YouTube, the world's largest video-sharing community . Viddy is aggressively expanding, though, hiring more engineers, building a web interface for watching videos, releasing an Android app, as well as adding better integration with social networks.
Yet what sets Viddy apart is its self-imposed 15-second limit, arguably its secret sauce, which mimics Twitter's 140-character max. "We're not setting out to make feature films here--15 seconds felt like the right place to start," O'Brien says. "It's a creative restraint: You'll capture the moment that really matters, in Twitter-style, bite-size web entertainment. Plus on mobile, we didn't think people would want to sit through long videos."
It's true. Fifteen seconds of Paris or Sheen feels like enough.
Read More: Cisco Kills Flip Cam, Abandons Consumer Strategy