There are several ways to interpret this question, and I'm not sure which you meant. Firstly, there is no version of CalendarDateSelect in Ruby's core or standard library. I'm sure the GUI frameworks available in Ruby (like Shoes) provide something similar, but I haven't used them enough to know much about it.
If you're referring to Rails, on the other hand, there are several date helpers available. The ones in Rails core are all select-menu-driven, but I know of at least a few plugins that allow you to add calendar controls to a Rails application with minimal code. There is indeed one called CalendarDateSelect, but I have not tried it personally (one of my co-workers wrote a different version which we tend to use).