What engines and tools will you recommend to build a prototype of knowledge-based question answering system?

What engines and tools will you recommend to build a prototype of knowledge-based question answering system?

I suggest looking into Ephyra, in particular OpenEphyra.  You might also like to check out my other answers under the Quora topic Question Answering Systems, such as:

• What are some good papers to read about Question Answering?