Highly configurable proof / disproof editor and calculator
Jape is a configurable graphical formal-proof calculator. It's possible to define a logic, decide how your users will view their proofs, and much more. It works with variants of the sequent calculus and natural deduction, as well as functional programming theories and theories of operational semantics.
Mac, Unix, Windows.
Jape is an incredibly useful teaching and formatting tool. Highly recommended.