Below is a list of projects which include functionality that is similar or related to sphinxcontrib-bibtex. If you know of any other, leave a message on the issue tracker.
Andrey Golovizin’s pybtex, a general purpose Python library for working with bibtex files. Drives sphinxcontrib-bibtex.
Matthew Brett’s bibstuff. Includes a Sphinx extension similar to sphinxcontrib-bibtex, as well as an assorted collection of bibtex tools. This is a fork of Dylan W. Schwilk and Alan G. Isaac’s dschwilk/bibstuff.
Weston Nielson’s sphinx-natbib. Similar to sphinxcontrib-bibtex but appears to be stalled in alpha stage. Interestingly, supports natbib-style citations. Apparently no longer maintained, and the original repository is no longer available. The most recent fork appears to be at github.com/f-i/sphinx-natbib.
Jeff Terrace’s Sphinx Thesis Resource sphinxtr, a fork of Sphinx which includes a fork of sphinx-natbib.