Microsoft is set to release the first preview version of Indigo, the new communications subsystem for Windows.

Set for general availability in 2006, Indigo is intended to make it easier for developers to build secure, reliable web services. The technology will be part of the next release of Windows, code-named Longhorn, but will also be available for Windows XP and Windows Server 2003, Microsoft has said.

The Indigo release is a "community technology preview" and precedes the first official beta test version, which is due by the end of June. While some of Microsoft's preview releases are not complete, this preview of Indigo includes all the features of the first beta, said Ari Bixhorn, a lead product manager at Microsoft.

"The community technology preview helps developers plan their development cycle by getting an early idea of how Indigo works," Bixhorn said. Additionally, Microsoft is looking for feedback on Indigo from developers, he said.

Indigo supersedes several technologies currently found in Windows and supports a range of WS-* Web services standards.

Along with the first preview release of Indigo, Microsoft will offer the latest public release of .Net Framework 2.0 and the second preview release of Avalon, the presentation subsystem for Longhorn. Avalon will also ship as an update to Windows XP and Windows Server 2003, Microsoft has said.

Microsoft claimed that the new Avalon preview would offer several advances over the previous version, including new controls, improvements to the layout system, performance improvements and enhanced support for XAML, which stands for XML application markup language and is a new way to describe graphical user interfaces in Windows.

The preview releases have been expected. Microsoft executives have been talking up the benefits of Indigo, Avalon and .Net Framework 2.0 at conferences. The company promises dramatic productivity gains with Indigo and the other technologies as developers will have less coding to do, while instead using "managed code."

The preview releases are available to subscribers of Microsoft's Developer Network. After the first preview and the first beta in the first half this year, the Indigo team plans to ship a second beta and will likely provide more preview releases before the final ship date sometime in 2006, Bixhorn said.