Daniel J. Velleman, author of "Howto Prove It" has Proof Designer

Proof Designer

If I remember correctly I think that was mentioned in his book.

Reading his book to go along with this would probably be very helpful.

I have hoped that a simple proof checker, something that was able to check each incremental step of the sort of simple proofs that beginning students might be writing and provide immediate feedback when it was either able to point out a flaw or was not able to see how to justify the latest step, and thus the step was probably incorrect or not well enough justified, might aid students enormously.

This would be very different from a research level question proof checker and very different from a research level theorem prover. Beginning students are not going to be doing either of those things. What I think beginning students need is immediate concrete feedback when they make little mistakes as they wade into the "cotton candy forest" where nothing seems certain at first in the transition from simple specific calculations to learning how to write proofs.