Recently I've been invited by the CrypTool team to contribute to the JCrypTool project. I've been following CryptTool for some time and it is definitely one of the best tools to practice and experiment with cryptography and cryptanalysis.
Looking at the latest JCrypTool version, it is apparent that there are vast design improvements, it is also more modular, which makes the extensibility of the project a very easy task. There are several algorithms to use, symmetric, assymetric, hash, MAC etc. So there are lots of things to play with!
In the Cryptanalysis part of the tool, there is a Columnar Transposition module, Frequency analysis graphs, aFriedman Test function and a Vigenere analyser/helper, so there is space for additions. Speaking of additions, I particularly like the plugins architecture in use, which makes the project very interesting indeed.