One of the projects I'm working on at home, IronCow, is now in a state of "somewhat usable alpha". It's a .NET API that allows developers to use Remember The Milk, the to-do list website, from any .NET language. IronCow is composed of two layers.
One layer is a "dumb" wrapper around the public REST API, in way very similar to what FlickrNet does with Flickr's own REST API. The second layer is a "rich" object model that exposes your tasks (and other data) through classes that stay in sync with the server as you manipulate them. This was done mainly with WPF applications in mind, enabling things like data binding and other reflection-based mechanisms.
IronCow is available on CodePlex.
A sample application that ships with IronCow is IronCow for Powershell. This is a Powershell snap-in that defines a few cmdlets that will let you manage your tasks through the command line! (if you don't see the point, or think it's lame, you're obviously not enough of a geek) You'll get to type command lines such as:
Get-RtmTask "dueBefore:tomorrow" | Sort Priority,Estimate | Export-Csv $Home\TasksToDoToday.csv
If that's not cool, I don't know what is.
This sample application is still a bit rough around the edges (understand: no installer - you need to compile and register the snap-in yourself, and no help file - you need to look at the code to know what parameters the cmdlets take!), but I'll focus on that once IronCow itself is stabilized. Stay tuned!