MTV is a plugin for WordPress that provides a new API for developing plugins and themes. Born out of frustration with the undocumented, inconsistent WordPress API, MTV provides a simple, familiar, consistent way to develop heavily customized WordPress sites.
MTV borrows a lot from existing MVC-style frameworks, namely Django and Backbone.js. If you're familiar with those frameworks, you should feel at home using MTV. If you're not familiar, go try some tutorials. It'll make you a better programmer.
This plugin hijacks and takes over how WordPress handles URLs and templates, and gives you new ORM-style tools for handling posts, users and blogs. This plugin does nothing by itself, and (hopefully) will not break stuff that you already have. It's just a set of tools for developers to use.
Get started by reading the wiki.