Adobe AIR isn't the only online-offline rich Internet app runtime. Curl, an enterprise rich Web app company that's been trying to break into the U.S. market after success in Asia, is releasing a beta version of its own competing runtime, Nitro, next week. Curl's actually had the capability to run applications offline and out of a browser since its first release, but doing so required substantial tinkering. Now, developers can create online-offline, out-of-browser Curl applications "as easily as browser-based Curl applications," according to Richard Monson-Haefel, Curl's vice president of developer relations.

Monson-Haefel says Curl sees itself as in direct competition with Adobe AIR for enterprise rich Internet apps. Adobe's AIR powers apps like eBay Desktop, which is an eBay-branded client application that mimics the functionality of eBay's Web site, but adds more graphical features and some offline cache.

Curl uses an object-oriented programming language, also called Curl, though developer can have panes in Curl applications that handle Flash, Flex, HTML, Ajax, or PDF by using, for example, a PDF viewer that's wrapped in some Curl code.

The company claims a few advantages over Adobe AIR, including performance, security and data access. Curl's own testing shows that Curl is 10 times faster than Adobe's ActionScript. It also includes a client database that's based on SQLite.

Adobe AIR applications are given full access to a user's underlying system, which potentially enables them to potentially install rootkits or do other harm. Microsoft, which has its own rich application plays with Windows Presentation Foundation and Silverlight, has repeatedly criticized Adobe AIR's security model. However, Curl forces its apps to generally run as unprivileged desktop apps with the same restrictions on accessing computer resources and networks as unprivileged browser applications or as quarantined applications that can only access, read and write to certain segments of a hard drive.