Private "storefronts" let corporations outfit employees with homegrown business apps.

FORTUNE -- Want to develop a small-molecule-based drug? There's an app for that. But you won't find it in Apple's App Store -- it's available only through a private storefront run by biotech giant Genentech.

The company, based in South San Francisco, Calif., has created some 20 mobile apps for its employees -- and a dozen more are in the works. In addition to highly specialized applications like Small Molecule Data Integration (a database of molecular compounds) there are generic ones such as the aptly named Get a Room, used for finding and booking conference rooms, and Peeps, an employee directory.

Genentech isn't alone. A growing number of companies -- from GE (GE) to IBM (IBM) to Standard Chartered -- are building customized corporate apps. (Think of them as mobile versions of the stuff you find on your company's intranet.)

The app-ification of corporate software is yet another example of how consumer behavior is influencing enterprise information technology: Executives who enjoy easy-to-use apps in their private lives are demanding the same tools in the workplace, often to the dismay of their IT departments, which must scramble to develop applications and get them onto employees' devices. "End users expect more," says Jeff Bipes, an IT manager for device maker Medtronic (MDT), which boasts 55 company apps. "They expect their apps to work better, and they expect to get them quickly."

The easiest way to distribute the software? An in-house application store that works much the way the Apple App Store or the Android Marketplace does, enabling users to simply download apps directly to their devices. Before Medtronic's company app store launched in January, Bipes said employees had to go through a cumbersome "sideloading" process -- dragging and dropping files into iTunes on their work PCs, then downloading them to their devices.

No one tracks the number of private apps (yet), but the mobile community smells opportunity: Late last year Apple (AAPL) opened up its iOS Enterprise Developer Program to any company willing to pay $299 a year. The program helps enterprises host and distribute iOS apps via corporate-branded storefronts, and offers technical support from Apple engineers.

Some tech departments work to accommodate employees' devices of choice. GE's mobile storefront, for example, offers apps for the iPhone, iPad, Android, and BlackBerry.

Employees say they like being able to browse and download apps easily, but surprisingly, some of the biggest fans of company app stores are beleaguered IT departments that like the secure nature of private app stores (the sites are password protected). Finally, a consumer-oriented technology that IT departments and employees can agree on.