Bowline: An MVC Framework for GUI Apps in Ruby
Unlike pure Ruby desktop libraries like Shoes, Bowline builds on Appcelerator Titanium, an SDK for building desktop apps that basically gives you a Webkit window and a set of APIs for interacting with various operating systems. This lets you develop for the desktop using familiar web technologies, including CSS3 and HTML5 (think Adobe Air!).
To allow your Ruby code to interact with your HTML, Bowline introduces the concept of "binders" which can update your views as the underlying data changes (a bit like controllers in Rails). Bowline also includes other ideas analogous to parts of the Rails framework, such as generators, helpers and models.
In this blog post Alex MacCaw shows off a simple Twitter client he built using Bowline - you can download it and continue to play on your own if you like. Nice work!