1. Grid System: The main difference between Skeleton and UIkit lies in their grid systems. Skeleton utilizes a simple 12-column grid system, making it easier for beginners to understand and work with. On the other hand, UIkit employs a more complex and versatile grid system that allows for more sophisticated layouts and designs.

2. Components and Modules: UIkit offers a wide range of pre-built components and modules that can be easily customized and integrated into projects. While Skeleton also provides basic styles and components, UIkit's library is more extensive and feature-rich, catering to a wider range of design needs.

3. Styling and Customization: UIkit offers more advanced styling and customization options compared to Skeleton. With UIkit, users have access to a variety of themes, styles, and utilities that allow for greater flexibility in design and layout.

4. JavaScript Components: UIkit includes a collection of ready-to-use JavaScript components that can enhance interactivity and functionality on a website. These components are not as comprehensive in Skeleton, making UIkit a more suitable choice for projects requiring advanced JavaScript functionality.

5. Documentation and Support: UIkit provides more extensive documentation and support resources, including tutorials, guides, and a community forum. This makes it easier for users to learn and troubleshoot issues while working with the framework, compared to the more limited resources available for Skeleton.

6. Community and Updates: UIkit has a larger and more active community of developers and designers, leading to more frequent updates, improvements, and new features being added to the framework. This ensures that UIkit remains up-to-date with the latest web design trends and technologies, giving users access to cutting-edge tools and capabilities.

In Summary, the key differences between Skeleton and UIkit lie in their grid systems, components, styling options, JavaScript functionality, documentation, and community support.