Rich Internet applications (RIA) are web applications that have the features and functionality of traditional desktop applications. RIAs typically transfer the processing necessary for the user interface to the web client but keep the bulk of the data (i.e., maintaining the state of the program, the data, etc.) back on the application server.

Benefits:

Although developing applications to run in a web browser is a much more limiting, difficult, and intricate process than developing a regular desktop application, the efforts are often justified because:

• installation footprint is smaller -- overhead for updating and distributing the application is trivial, or significantly reduced compared to a desktop or OS native application
• updates/upgrades to new versions can be automatic or transparent to the end user
• users can use the application from any computer with an internet connection
• many tools exist to allow off-line use of applications, such as Adobe AIR, Google Gears, and other technologies
• most RIA techologies allow the user experience to be consistent, regardless of what operating system the client.
• web-based applications are generally less prone to viral infection than running an actual executable

Because RIAs employ a client engine to interact with the user, they are:

• Richer: They can offer user-interface behaviors not obtainable using only the HTML widgets available to standard browser-based Web applications. This richer functionality may include anything that can be implemented in the technology being used on the client side, including drag and drop, using a slider to change data, calculations performed only by the client and which do not need to be sent back to the server, for example, a mortgage calculator.
• More responsive: The interface behaviors are typically much more responsive than those of a standard Web browser that must always interact with a remote server.

The most sophisticated examples of RIAs exhibit a look and feel approaching that of a desktop environment. Using a client engine can also produce other performance benefits:

• Client/Server balance: The demand for client and server computing resources is better balanced, so that the Web server need not be the workhorse that it is with a traditional Web application. This frees server resources, allowing the same server hardware to handle more client sessions concurrently.
• Asynchronous communication: The client engine can interact with the server without waiting for the user to perform an interface action such as clicking on a button or link. This allows the user to view and interact with the page asynchronously from the client engine's communication with the server. This option allows RIA designers to move data between the client and the server without making the user wait. Perhaps the most common application of this is pre-fetching data, in which an application anticipates a future need for certain data and downloads it to the client before the user requests it, thereby speeding up a subsequent response. Google Maps uses this technique to load adjacent map segments to the client before the user scrolls them into view.
• Network efficiency: The network traffic may also be significantly reduced because an application-specific client engine can be more intelligent than a standard Web browser when deciding what data needs to be exchanged with servers. This can speed up individual requests or responses because less data is being transferred for each interaction, and overall network load is reduced. However, over-use of asynchronous calls and pre-fetching techniques can neutralize or even reverse this potential benefit. Because the code cannot anticipate exactly what every user will do next, it is common for such techniques to download extra data, not all of which is actually needed, to many or all clients.