Today, Huw Collingbourne - developer of Ruby In Steel, a family of Ruby and Rails IDEs for Windows - has
launched Ruby In Steel Personal Edition (PE), a free Ruby and Rails IDE built around Microsoft Visual Studio 2008.
Previously, Huw had focused heavily on his commercial offerings (still available, and providing exclusive features such as the high speed "Cylon" debugger), but Ruby In Steel PE is truly free (as in beer). It includes the shell edition of Visual Studio 2008, Ruby, Rails, MySQL, and Ruby In Steel itself. There's no registration required and no timeouts, and it's packaged as a simple all-in-one installer (clocking in at 175MB).
If you're a Windows-based Ruby developer not using Ruby In Steel already, check it out. It's an excellent choice if you want a Windows-based Ruby and Rails development tools solution in a single package.
Disclaimer: I have had access to licensed versions of Ruby In Steel in the past for review purposes, but there are no commercial motivations to mention the product. This is a purely editorial recommendation.