Pyke [1], a Python based rules engine, supports both forward and backwards chaining. The docs are good. We used it in an AI class I was a TA for; the previous years used Prolog and everyone (most everyone) consistently hated Prolog.... For students used to the video games that are IDEs these days, SWI Prolog and its UI is awful. Pyke and PyKnow were well received, however. As it is Python based, it is a lot easier to deal with than Prolog.

[1] http://pyke.sourceforge.net/index.html