4 links
NuPrl Proof Development System
cs.cornell.edu
A powerful tactic-based proof assistant, developed over the last 15 years at Cornell University. IFeatures include: very expressive logical language based on Martin-Lof type theory…
The HOL Theorem Proving System
hol.sourceforge.net
The system documented originated at the Laboratory for Applied Logic of Brigham Young University and features higher-order, classical, natural deduction with tactics.
The LEGO Proof Assistant
dcs.ed.ac.uk
A powerful tool for interactive proof development in the natural deduction style. It supports refinement proof as a basic operation. The system design emphasizes removing the more …