Hosted on CodePlex.com this project aims to take guidance from Microsoft and marry it with the CodePlex community. In the projects own words:
The App Arch guide provides design-level guidance for the architecture and design of applications built on the .NET Framework. It focuses on the most common types of applications, partitioning application functionality into layers, components, and services, and walks through their key design characteristics.This guide is a collaborative effort between patterns & practices, product teams, and industry experts
It's a great idea, but like with all community projects it depends on contribution by the public. I am eager to see this one develop over time.