Selenium is specifically designed for automating web applications for testing purposes. It provides tools and libraries to interact with web browsers and automate web application testing tasks. Here are key points about the type of applications Selenium can test:

1. Web Applications: Selenium tests any application that can be accessed through a web browser. It simulates user interactions with web elements like buttons, forms, input fields, and navigates through web pages just like a real user.

2. Cross-Browser Testing: Selenium supports multiple browsers, such as Chrome, Firefox, Internet Explorer, Edge, and Safari. This allows for cross-browser testing to ensure that web applications function correctly across different web browsers.

3. Responsive Web Design Testing: Selenium can also be used to test the responsiveness of web applications across various devices and screen resolutions.

4. Rich Internet Applications (RIA): Selenium can test applications built using technologies like Ajax and JavaScript.

5. Limited Mobile Web Application Testing: While Selenium is primarily for web applications, it can also be used to test mobile web applications through mobile browsers. However, for native or hybrid mobile app testing, other tools like Appium (which extends Selenium) are more suitable.