This is my most recent attempt at a Rails+HEYU-based x10 controller. As of right now it is not particularly functional, so I'd advise against using it.
Ultimately, you'll need to install this on a Rails-ready server along with HEYU, and then you'll be able to use it.
Short answer, because I like building things. Long answer, because none of the X10 libraries I've found have decent APIs, and that's something Rails in particular does really well!