The Dextop application framework allows you to create Rich Internet Applications based on .NET/Mono and Sencha Ext JS. It has proven to be useful for online business applications. It features a desktop-like Ext JS frontend, simplified client-server communication, a stateful programming model, real-time updates and notifications from the server, automatic column model generation, automatic store model generation, and automatic form generation.
Minitube is a YouTube application for Mac, Linux, and Windows. With it, you can watch YouTube videos in a new way: you type a keyword, and Minitube gives you an endless video stream. Minitube does not require the Flash Player. It is not about cloning the original YouTube Web interface, but strives to create a new TV-like experience.