For the official intro please see lively-next.org
lively.next is a web-based personal construction kit and development environment. Its user interface allows direct manipulation, composition, and behavior modification of objects similar to Smalltalk and Self. User content (workspaces and individual objects) are fully serializable so that users can simply create snapshots of their work, either for later retrieval or collaboration.
In the tradition of Smalltalk systems, lively.next is fully implemented in itself (client as well as server parts) and the entire system can be inspected and modified on the fly. This enables very short turn-around time for new features and makes for a joyful development experience.
Lively can be used for rapid prototyping or as a full-scale development environment that integrates well with third party systems. To learn more about lively.next visit the project page or dive into the live system.