There is one for AsciiDoc Python which was created by Dag Wieers. It builds a flat OpenOffice text document (XML), which can be opened or imported into LibreOffice.
Greg Turnquist used this as the basis for a backend for Packt Publishing, which he posted about on the list a few days ago. I got him started porting this backend to Asciidoctor. You can find both efforts in the following repository:
(At the time of this post, the beginning of the Asciidoctor backend is in a pull request).
Once you get the gist of how the backend works, you should be able to make any OpenOffice document you want.
-Dan