Famo.us is a JavaScript framework designed to help developers create complex and smooth UIs within web browsers by offering an open-source 3D layout engine integrated with a 3D physics animation engine capable of rendering DOM, Canvas, and WebGL. The framework's "Mixed Mode" allows developers to enhance performance by offloading tasks to the GPU, such as rendering an orbiting orb with WebGL in a browser-based game or creating a robust drop shadow for web elements, which would otherwise be resource-intensive with CSS3. This blend of technologies facilitates the construction of high-performing, visually appealing applications directly within the browser environment, with Famo.us providing demos and resources for further exploration, including integration with AngularJS.