1. 1. Architecture Differences: Fabric.js is based on a retained mode graphics system, where all objects are kept in memory and rendered at each frame. On the other hand, Two.js uses an immediate mode rendering system, where objects are drawn directly to the canvas whenever needed. This architectural difference gives Fabric.js more flexibility for complex scenes with frequent updates, while Two.js provides better performance for simple and static scenes.

2. 2. Vector vs SVG Graphics: Fabric.js focuses on manipulating vector graphics using its own object model, with support for standard shapes and paths. Meanwhile, Two.js primarily uses SVG as its graphics technology, allowing developers to take advantage of the numerous built-in SVG features and libraries available. This difference makes Fabric.js more suitable for custom graphics creation, while Two.js excels in integrating with existing SVG assets.

3. 3. Animation Capabilities: Fabric.js provides a built-in animation framework, with support for tweening and timeline-based animations. This allows for smooth and dynamic animations of objects and their properties. In contrast, Two.js does not have a built-in animation system and relies on external libraries like GreenSock or Anime.js for animated effects. Fabric.js is a more self-contained solution for animations, while Two.js offers more flexibility by supporting various animation libraries.

4. 4. Interactivity Support: Fabric.js provides a robust interactivity model, making it easy to handle user interactions such as clicks, mouse movements, and touch events. It also offers a selection and interaction handling system by default, which simplifies the implementation of interactive features. Two.js, on the other hand, focuses more on graphical rendering and does not have extensive built-in support for interactivity. It leaves the handling of user interactions to the developers, providing a more flexible but potentially more complex approach.

5. 5. Backward Compatibility and Browser Support: Fabric.js prioritizes backward compatibility and supports a wide range of browsers, including older versions. It ensures that code written for previous versions remains functional in newer releases. Two.js, on the other hand, focuses on utilizing modern web technologies and may not provide full support for some older browsers or their specific features. Fabric.js is a more suitable choice for projects requiring broad compatibility, while Two.js caters to the latest web development standards.

6. 6. Community and Documentation: Fabric.js has a large and active community, with extensive documentation and resources available. This means developers can find help and examples easily when working with Fabric.js. Two.js, although still popular, has a smaller community compared to Fabric.js. While the official documentation for Two.js is comprehensive, accessing additional resources or community support may require more effort.

In Summary, Fabric.js and Two.js differ in their architecture, graphics approach, animation capabilities, interactivity support, browser compatibility, and community size. Fabric.js offers a retained mode graphics system, customizable vector graphics, built-in animation framework, robust interactivity support, backward compatibility, and has a larger community. Two.js utilizes immediate mode rendering, focuses on SVG graphics, relies on external libraries for animations, provides more flexibility for interactivity, may have limited backward compatibility, and has a smaller community.