Sideline, announced on the Yahoo user interface blog, is a desktop application that displays real-time mentions of specific keywords, brands, or names. It is capable of custom search groups, advanced queries, and refreshes the application with new mentions automatically. How does it do this? It pulls keyword mentions from Twitter, of course!
The Yahoo Sideline project seems to have grown out of an internal project over at Yahoo, the goal of which was to create a desktop application that utilized Twitter, would be compatible with Mac OS X, Windows, and Linux with minimal work, and didn't require learning new programming languages. The result was an Adobe AIR application, which allows for the building of apps in Web-specific languages, such as PHP, HTML, and Javascript.
The actual application is simple and replicates much of the functionality of other Web-based Twitter apps, such as monitter. It highlights and tracks keywords, is easy to search, and according to Yahoo, offers "20% more awesomeness." Sideline seems to be more of a research project for Yahoo rather than building a new major new product or division.
The Yahoo User Interface team also included in its announcement some suggestions for Adobe AIR app development, primarily that developers need to understand their programming environment and debugging tools are absolutely essential. Sideline is open source, so developers are welcome to play around with the code.