Final answer:
The distinguishing feature of a rich Internet application is its complexity, which mirrors traditional software while being accessible within a web browser without needing local installation.
Step-by-step explanation:
A rich Internet application (RIA) stands out due to its intricate functionality, mirroring the complexity of traditional software. What sets RIAs apart is their ability to deliver robust features and capabilities, typically associated with desktop applications, all within the confines of a web browser. This eliminates the need for local installation, offering users a streamlined and accessible experience. The distinguishing feature lies in the sophisticated tasks and functionalities that RIAs can perform, akin to traditional software, making them a powerful and versatile choice for web-based applications. In essence, the complexity of traditional software seamlessly converges with the convenience of web accessibility in the realm of rich Internet applications.