Calendar Date Select is semi-light-weight Free Rails Calendar Date Picker Script. Its about about ~20k of javascript/css in size. It takes full advantage of the prototype.js, a free JavaScript library, resulting in less code, but maintaining a great deal of functionality.
This free Javascript Date Calendar Picker can be used as a pop-up date picker and as ab embedded calendar. Calendar Date Select is easy to install, use and localize.
Read a small tutorial here on how to use a different format other than the default. Also, how to implement your own date format, if one provided does not meet your needs.
Requirements: rails 2.0 or greater