Adobe Systems has unveiled Apollo, an intriguing new runtime code project: It gives users an alternative for building Web-based applications that can also run on the desktop independent of a browser. Apollo lets rich Internet applications run offline, and it could threaten the popularity of programming platforms such as Java and Microsoft’s .Net, Adobe says. Apollo, like Flash Player, is a runtime applet, but one in which applications built using standard Internet development technologies (such as HTML, Flash and Ajax) can run without a live Net connection.

Adobe seems to be taking a run at Microsoft, which has been ramping up its own strategy to give developers tools for building Web applications. Microsoft has been trying to tie those applications to its Windows desktop OS and development environment.

Adobe released an alpha version of Apollo on its Adobe Labs site in March; developers can download this and a software development kit for free. Look for a full release later this year, says Kevin Lynch, senior VP and chief software architect for Adobe.

One example of Apollo in action: Consultancy EffectiveUI used Apollo to build a desktop application for eBay that lets eBay’s auction site run on the desktop without being connected to the Internet or accessed through a browser.

Notably, Web applications built with Apollo will automatically update to the Web any information that a user has added to the application while offline. As soon as the user reconnects to the Internet, the update proceeds, with no extra action required by the user.