On the top floor of a bland high-rise in downtown Austin, the city's future is being written—or, more accurately, coded. In the gutted shell of a once-staid office, now colonized by giant beanbags and quirky light fixtures, entrepreneurs in T-shirts hack away in podlike clusters of workstations, striving to develop the next big mobile app, cloud data service, e-commerce platform, or other piece of hit software.

The 150 or so companies that rent space here at Capital Factory, one of Austin's many startup incubators, have reason to be hopeful. The recent IPOs of some of their local peers, including Bazaarvoice and HomeAway, have raised hundreds of millions of dollars. In the process, they have also netted the kind of attention typically reserved for a breakout performance at the annual South by Southwest music showcase. In a town synonymous with bands, the tech nerds are making noise.