This is a big year for South by Southwest. On March 11, the Austin music and media festival and trade show celebrates its 25th anniversary. Since Roland Swenson founded the festival in 1987, it has launched the careers of promising young musicians and, more recently, more than a few up-and-coming businesses. In 2009, Foursquare publicly launched there, kicking off the geolocation craze. Two years earlier, Twitter, a virtual unknown at the time, caught fire at the festival. So, what's next? We scoured the list of attendees and found plenty of promise. This year's crop may not include the next Twitter, but you never know. Here are four especially intriguing app-based businesses:

A free smartphone travel app, iTourU allows anyone to record audio tours, tag routes and landmarks on a map, add text and photos, and share it all with anyone else who is using the app. Founded by Andrew Dever, a native of Canberra, Australia, the service also lets travelers vote on their favorite tours and get recommendations from friends. More than 60 free tours in Australia, India, and North and South America are available on iTourU, and Dever hopes to open an iTourU marketplace as part of the app. In the marketplace, established travel guide publishers and tourist attractions will sell audio tours and give iTourU a cut of the sales. One hurdle for consumers: the cost of data roaming while abroad.

Blue Calypso
Companies are constantly looking for ways to promote their brands through their customers' social networks. Dallas-based Blue Calypso will work with them to build ad campaigns that consumers will tell their friends about in return for rewards. It works like this: Users who download the free app, called Calyp, see a list of campaigns tailored to their interests. Music fans, for instance, might see campaigns advertising tickets to upcoming rock concerts. Consumers can spread the campaign through Facebook posts or Twitter feeds or by text message—and when they do so, they earn cash on a Blue Calypso prepaid debit card. Since the company, founded by Andrew Levi, launched a beta version last November, users have made an average of $75 a month. (The company limits users' promotions to four a day in an attempt to control spamming.) The campaigns cost advertisers a minimum of $500, depending on how long they run and how many consumers they reach.

With this social networking website and mobile app, users post tweetlike updates about their activities. These could include competing in a triathlon or learning how to play the violin. Friends and followers then award users points. The more impressed the friends and followers are, the more points they can award, up to 50 each. Once users have a certain number of points, they are eligible for prizes, including bumper stickers and sporting equipment. LifeKraze is ad supported and free for users, who receive additional points when they view ads. The company, based in Chattanooga and founded by Ben Wagner, David Nielson, and Michael Brooks Jr., is in partnership talks with Nike and Coke.

The original version of this article included a description of the mobile app company, That company subsequently announced it was pulling out of the festival after Inc. went to press and was, therefore, removed from this article.