Lojban is a constructed language based on predicate logic. I like it because it would make a ideal language as an intermediary between humans and computers. The Logical Language Group's Lojban site will tell you much more about the subject.
I co-authored the Lojban speech module for Festival (still in alpha). See the sample on the Lojban wiki.
Before that, I tried my hand at making a Lojban text-to-speech voice for Festival using the American voice.
A keyboard map for Yudit that lets you write lojban encoded in Tengwar.