1. Test Execution: Cypress runs directly in the browser and operates in the same run-loop as the application being tested. This allows it to have full control over the entire testing process, including network traffic, DOM manipulation, and browser events. On the other hand, Geb operates outside the browser using WebDriver, which communicates with the browser through a separate process. This can sometimes lead to synchronization issues between the tests and the browser.

2. Testing Paradigm: Cypress follows a synchronous testing paradigm, where each command is executed one after the other in a single run-loop. This makes it easier to write and understand tests, as there are no callbacks or promises involved. Geb, on the other hand, follows an asynchronous testing paradigm, where commands are executed asynchronously and the test writer needs to handle promises and callbacks. This can make the test code more complex and harder to maintain.

3. Language Support: Cypress is primarily built for JavaScript-based projects and has excellent support for testing applications written in JavaScript. It also has limited support for other languages like TypeScript. Geb, on the other hand, is built on top of the Groovy programming language and is mainly used for testing applications written in languages that run on the Java Virtual Machine (JVM), such as Java, Groovy, and Scala.

4. Integration with Testing Frameworks: Cypress is a complete end-to-end testing solution and does not require any additional testing frameworks or libraries. It has its own assertion library and mocking/stubbing capabilities built-in. In contrast, Geb works seamlessly with popular testing frameworks like JUnit and Spock, allowing test writers to leverage existing test runners and make use of their favorite assertion libraries.

5. Automatic Retries: Cypress has built-in automatic retrying functionality, which means that if a command fails due to a timing issue, Cypress will automatically retry the command until it passes or times out. This can help reduce flaky tests caused by transient network or timing issues. Geb, on the other hand, does not have this automatic retry mechanism, and the test writer needs to implement their own retry logic if needed.

6. Community and Ecosystem: Cypress has gained significant popularity in the testing community and has a vibrant ecosystem with a wide range of plugins and community-contributed resources. It also has excellent documentation and a large active community for support. Geb, although not as widely popular as Cypress, still has an active community and a decent ecosystem with plugins and resources available.

In summary, Cypress and Geb have key differences in their test execution approach, testing paradigm, language support, integration with testing frameworks, automatic retrying functionality, and community/ecosystem support.