I was initially baffled when I looked for the Nitro extensions in the current Curl IDE documentation. Then I looked at the source code for the three Nitro samples supplied on the Curl Web site, and that made it clear where to find the Nitro functions in the Curl libraries. One of the Nitro samples did not work for me, however, because of a problem with the Facebook API. The other two samples worked very well.
The Curl RTE (runtime environment) runs on Windows, Mac OS X and four versions of Linux. The Curl IDE runs on Windows and Linux. The Curl development plug-ins for Eclipse work with Eclipse 3.3 and 3.4 on Windows and Linux platforms.
The base Curl IDE and runtime that include Nitro are free, as are deployment licenses for publicly available, free Web sites that use the base capabilities. A Curl Pro/Deployment license starts at US$12,000; Curl has pricing models designed for enterprise, Internet, software-as-a-service and reseller business models.
Basically, Google Gears is a way to take Web applications offline in a browser. Curl Nitro and Adobe Air can go one step farther and dispense with the browser.
The online Gears developer documentation discusses Version 0.5, released a month ago. It includes nine samples that illustrate the use of the APIs. You can download the source to all of these samples, plus some articles, a couple of tools and an Apache mod implementing the resumable HTTP request proposal. One of the articles is a tutorial on taking Web applications offline with Gears, written by Omar Kilani of Remember The Milk . Kilani and his team implemented offline functionality for their application in "four caffeine-fueled days."