The LaTeX package bussproofs.sty for typesetting natural deduction/sequent calculus proofs is nifty especially for its nice alignment of sequents. By contrast to the proof.sty package, it doesn't allow you to typeset missing parts of a proof, though. proofs.sty has the \deduce command for that; it typesets vertical dots instead of a horizontal inference line.
I wrote an add-on for bussproofs.sty that does the same. Not quite ready for prime time yet, but if you like playing with bleeding-edge stuff, you can get it here. Feedback? Please file an issue on github.