MikeRiedel 

Provides simple handling of transient errors that can occur with any network communication. Retries, intervals, mapping and detection can all be fully customized. Built-in handlers are provided for WCF, WebClient, HttpRequest. Supports .NET 4 and later, Silverlight 4 and 5, Windows Store Apps, and... More information

An MVVM toolkit that enables you to share the code and XAML files (unchanged!) between WPF and Silverlight and Windows Store Apps

Extremely lightweight and efficient yet complete implementation of a Hierarchical State Machine. Supports .NET 4 and later, Silverlight 4 and 5, Windows Store Apps, and Windows Phone 7 and later.

Simple cross-platform locks. Supports .NET 4 and later, Silverlight 4 and 5, Windows Store Apps, and Windows Phone 7 and later.

Storage made simple, fast and easy across platforms. Supports .NET 4 and later, Silverlight 4 and 5, Windows Store Apps, and Windows Phone 7 and later.

Provides shims for for functionality gaps across .NET, Windows Phone, Windows Store Apps and Silverlight.