NuPrl Proof Development System
A powerful tactic-based proof assistant, developed over the last 15 years at Cornell University. Features include: very expressive logical language based on Martin-Lof type theory, extensive library of formal mathematics and automata theory, possibility of an extraction a certified program from the constructive proof of its formal specification, graphical proof editor. NuPrl was successfully used in verifying components of the Ensemble group communications system.