Cosas is a web emulation of the GTD app Things. My plan is to use the web interface at work where I can't use my phone. There will also be an implementation for the iPhone, Android and perhaps a thick client if the mood strikes me. The web interface is written using Ext/JS 4 and all information will be updated using tiny AJAX calls. This is because I want the back end to be as simple as possible to re-implement using whatever framework that is most convenient.