(Business 2.0) – As a software industry analyst, Stephen O'Grady has attended nearly 200 technology conferences. But that doesn't mean he's enjoyed them. His biggest complaint: The topics tend to be chosen by the sponsors rather than the "folks who drive my research"--software developers. But that changed in February when O'Grady arrived at Mashup Camp, an exclusive two-day gathering of Silicon Valley geeks billed as an "unconference."

Attendance was free but limited to the first 300 people to sign up on the Mashup Camp wiki. The Computer History Museum in Mountain View, Calif., donated space in exchange for a Wi-Fi network. Though the event had sponsors like Sun Microsystems, its agenda was created on the fly by attendees. As chaotic as that sounds, it sparked a ton of ideas. "The ratio of signal to noise was outstanding," O'Grady says, "the best of any conference I've been to."

Welcome to the weird world of unconferences, a trend that is shaking up the $122 billion conference industry. These inexpensive, informal gatherings--like BarCamp, BrainJams, and Foo Camp--are conceived as little as weeks in advance. All were started in the past few years by Valley types bored with the usual calendar of confabs. "We figured there was much more expertise in the audience than there possibly could be onstage," says BarCamp co-founder Ryan King.

Unconferences break the barrier between the two. Attendees write topics they're interested in on boards, consolidate the topics, and then break into discussion groups. At traditional conferences, the most productive moments often occur in the corridor between meetings; at unconferences, attendees like to say, it's all corridor.

The result attracts engineers and executives from Adobe, eBay, Google, Microsoft, and Yahoo. Some companies are even comfortable enough to show upcoming products. Redwood City-based Riya, whose photo-recognition software won best of show this year at the prestigious Demo conference, actually unveiled it four months earlier at an unconference, TechCrunch Party 4.

Now the concept is spreading far beyond Silicon Valley. This year has seen a BarCamp in Bangalore and a Mashup Camp in Nanjing. Walt Disney Co. employees who attended Foo Camp, organized by publisher Tim O'Reilly, created an in-house version: Pooh Camp. The result so impressed Disney chiefs that a second Pooh Camp is expected this fall.

The conference business is unlikely to go away, but big-budget events are now being paired with ad hoc counterparts. This month's high-tech Supernova conference in San Francisco asked three unconference organizers to create complementary events--something that should make attendees like O'Grady much happier.

HOW TO HOST AN UNCONFERENCE

1 Create a wiki so attendees can sign up and discuss proposed topics. See BarCamp.org and BrainJams.org for help with wiki setup.

2 Find sponsors that are willing to assist without interfering. Unconference sponsors have donated everything from lunch to the venue itself.

3 Post author Harrison Owen's Law of Two Feet: Any person neither learning from nor contributing to a group discussion must walk to another one.