Windows Phone Foundations?
Windows Phone Foundations is simply a collection of Open Source Projects which make windows phone development nicer for experienced developers. Making testing easier, giving out of the box IoC support and allowing you to use common patterns like MVC or MVP with ease.
The reason for bringing multiple frameworks together in a single place is we want to try and push the idea that you can have two frameworks, which both achieve the same goals, have a similar feature set but one uses the MVP pattern, one uses the MVC pattern.
Powering both Windows Phone MVC and Windows Phone MVP is a library called Windows Phone Essentials! The essentials project has a heap of helpers, abstractions (think System.Web.Abstractions but for the phone) and much more.
Windows Phone Essentials
Focused on common helpers, testing and code related tasks, rather than another controls library
Windows Phone MVC
An MVC implementation for WP7, inspired by ASP.NET MVC and Magellan
Windows Phone MVP
An MVP implementation for WP7, inspired by http://webformsmvp.com/
MetroPimp
An API for pushing notifications to WP7 devices using Microsoft Push Notification Services (MPNS).