A simple tool that I wrote in my first semester to experiment with substitution ciphers.
Back in 2011 in my first class on cryptography we were give a ciphertext that was encrypted using a simple substitution cipher. After I had manually cracked the problem using frequency analysis, I hacked together this programm in order facilitate the task in the future.
This is not something you frequently need unless you teach beginners historic cryptography or for very simple CTF exercises.