Spline is a 3D design tool that allows users to create and collaborate on 3D designs directly in their web browser. It offers real-time collaboration where multiple users can work on a design simultaneously. Some of its main features include 3D modeling, animation, materials, physics simulation, and game controls. Spline also makes it easy to integrate 3D designs into other projects and export them as images, videos or 3D files. Spline is a simple yet powerful tool for 3D design that individuals and teams can use. It provides examples of designs and testimonials from users in different fields like product design and UX. Overall, Spline is a browser-based platform for creating, sharing, and interacting with 3D content.