Adding easily animatable views, performance optimizations like view caching, and creating something that has a root view, long before the big frameworks did so, was a lot of fun and hard work. However, this is dated and MVC based - not nearly as nice as the much improved component based structure we have now and improved state management.
Vesel is work in progress framework for building Single Page Applications that are designed for mobile devices with transitions and animations baked into the core (see AnimView).
Vesel is currently a part of a project and a work-in-progress framework. Internally this is the base javascript project for the Heads Up webapp, but once its complete plans are to open source this to make everyones lives easier. Vesel is currently a combination of Thorax + Lumbar.