Rails is an open source, cross-platform, full-stack, Model-View-Controller (MVC) framework for the Agile development of database-driven Web applications that use the Ruby language. This dense definition incorporates quite a few concepts that you may not be familiar with. Let's break things down so as to get a better overview of the framework.
Rails is an open source project. It's released under a very liberal license (MIT) that enables you to freely modify, contribute, and distribute the framework. In the vernacular of the Free Software world, Rails is free as in beer and as in speech. As a Microsoft developer, you're probably used to proprietary software, where several of the components that you employ in your applications are closed source.
The fact that Rails is open source implies that, whenever you encounter a bug in the framework itself, you'll have full access to the source code of the libraries that constitute the framework. You will be able to identify where the problem lies, report it with accuracy, and even correct it yourself and submit a patch to the project. In other words, stepping through and reviewing the source code helps you to better understand how the framework operates and in turn enables you to build better applications.
Unlike ASP.NET (with an exception made for its alternative implementation through the Mono project), Rails runs on a number of platforms. The most popular choices within the ...