1. Syntax and Usage: Fluent Assertions provides a fluent and intuitive syntax for creating assertions, making it easy to read and understand. On the other hand, Robot Framework relies on a simplified high-level language with a keyword-driven structure, allowing for easy creation of test cases without the need for programming skills.

2. Integration: Fluent Assertions is specifically designed for .NET applications and integrates seamlessly with popular testing frameworks such as NUnit and xUnit. On the contrary, Robot Framework is a more versatile tool that can be used for testing applications written in different programming languages and platforms.

3. Extensibility: Fluent Assertions offers a wide range of extension points, allowing developers to add custom assertions and tailor the library to their specific needs. In contrast, Robot Framework provides a set of built-in keywords but also allows users to define their own custom keywords for additional functionality.

4. Test Data Handling: Fluent Assertions primarily focuses on providing expressive and readable assertions. It doesn't have built-in capabilities for managing test data or test case execution flow. In contrast, Robot Framework has extensive support for test data handling, including variable substitution, data-driven testing, and test case management.

5. Reporting and Logging: Fluent Assertions doesn't provide built-in reporting or logging capabilities. It relies on the underlying testing framework for reporting test results. However, Robot Framework includes built-in support for generating detailed test case reports and logs, making it easier to analyze test results and track issues.

6. Community and Support: Fluent Assertions is widely used in the .NET community and has an active and supportive community of developers. It has comprehensive documentation and regular updates. Robot Framework, being open-source, also has a strong community and active development. It has a rich ecosystem of libraries and plugins contributed by the community.

In summary, Fluent Assertions provides a fluent and intuitive syntax for creating test assertions in .NET applications, while Robot Framework is a versatile test automation framework with a keyword-driven approach, supporting various platforms and programming languages. Fluent Assertions focuses on readability and maintainability, while Robot Framework provides extensive support for test data handling and reporting. Both tools have active communities and offer different features based on specific testing needs.