I've been looking at this: http://www.spontaneousderivation.com/2008/12/29/state-of-the-union-a-very-basic-ruby-epub-library/ but it's pretty basic, to the point that it might just be smarter to roll my own solution. I also found eeepub, which seems to be the most recent.
Anyone know of any other gems or libraries for creating epubs?
You could check https://github.com/glejeune/jekyll-epub and https://github.com/jlapier/epubbery.