There is a 3rd-party Ruby (and Rails) developer capability built on top of Visual Studio. It's called Ruby In Steel - you can find it here http://www.sapphiresteel.com .
This is one of those deals where you license Visual Studio, then you license the Ruby In Steel thing, and off you go. But the problem is, for Ruby devs, sometimes the initial license fees are a bit pricey. For license cost reasons alone, they sometimes look elsewhere (sniff sniff!) for their Ruby IDE.
Now comes word from the Ruby In Steel people that they are extermely interested in the VS Shell. They want to offer a low-cost 'all in one' edition of Ruby In Steel for those poeple who don't have Visual Studio for cost reasons.
For those who are not clear on what the Visual Studio Shell is, see here. Imagine Visual Studio, stripped of its compiler support, its debugger, the project management stuff. With all this stuff removed, it is a "shell" of its former self. This is VS Shell in isolated mode. One way to think about it - it is basically a blank slate user interface - it has menus, menu items, movable and dockable panels, collapsible lists, property sheets, a graphical design framework, and so on - but they are all blank. So if you want to build a designer, for anything, you can use VS Shell as the starting point. And it's a royalty-free license. There is also an integrated mode for VS Shell, and that's interesting if you want to use VS Shell to merge with any install of Visual Studio on the system. This is particularly interesting to companies who want to provide programming tools built on Visual Studio.
Anyway, if you are interested in developing Ruby in Visual Studio connect with the Ruby in Steel people or get back to me here on this blgo and I'll connect you.
On a related note, if you are a Ruby fan, you might also check out IronRuby, which is an implementation of Ruby on the .NET CLR (DLR).