Web applications are typically presented as a series of HTML pages, with one limited thing happening per page. Doing something simple, such as buying a book, can take seven or eight screens.

To get Web applications to function more like software on a desktop, companies have started embracing a new class of user-interface technology that emerged over the last two years called rich clients. They can be built atop a Web application and combine many of its functions onto a single page.

Initially aimed at consumers, these rich clients are finding their way inside companies, opening the door to easier-to-use, more powerful applications.

At Zones Inc., an online computer seller, an account manager can view customer data alongside order-history data, though they reside in different back-office applications. Zones put a rich-client front end over the Java code the company wrote to extract data from an Ecometry Corp. mainframe order system and an Onyx Corp. customer-data system. "We previously had to use each system separately," says Brian Tallon, director of E-commerce at Zones. An account manager talking to a customer would toggle furiously between the screens of each application to find the order information and relate it to the customer's status.

Using Macromedia Inc.'s Flex user-interface components, that customer and order data are presented side by side. And unlike HTML pages with their rigid structure, quarter-segments of the screen expand to show options for digging deeper into the data, Tallon says.

Rob Carpenter, chief technology officer at Dorado Corp., a builder of business-to-business applications for the mortgage industry, uses Flex for a rich-client interface for other reasons. With a rich client, a mortgage underwriter and a credit risk manager at a bank can get different views of a customer's financial data based on their respective roles, even though the information comes from the same source. When one of them moves down a list to select a new customer, his screen layout remains the same but gets repopulated automatically with new data from the server. An HTML application would have to download a fresh page, with all its tagged structure, instead of just the data, Carpenter says.

In early November, Macromedia will upgrade the 6-month-old Flex 1.0 to release 1.5. It will be priced at $12,000 for a two-CPU server production version.

Macromedia has plenty of competition, including smaller companies developing innovative rich-client products. One of the most prominent, DreamFactory Software Inc., made a user interface for Salesforce.com Inc.'s online applications, allowing Salesforce customers to customize what their sales representatives see. Other players include Laszlo Systems, which just made its rich-client Laszlo platform available as open-source code, Nexaweb Technologies, and Altio.

Building rich-client applications often requires learning to use new tools, but users say it's less complicated than building the same interface in Java or Microsoft .Net. Choice Homes Inc., a homebuilder in Dallas and Atlanta, uses Flex for its online Family Market, where employees spend company vouchers they've earned on apparel with Choice Homes logos. Developers saved 15% of the time needed to build the user interface using Flex and MXML, a Macromedia version of XML with proprietary tags, says Tim Farmer, manager of the software architect team.

Java programmers quickly picked up how to use MXML and the Flex components, Tallon says. Without them, he says, inserting function-rich features such as drag-and-drop capabilities and chart options into the app would have been difficult or impossible with HTML.