GPU version, now known simply v5700 bitcoin wiki hashcat. 00, is released as open source software under the MIT license.
01 before it was replaced by hashcat. It was designed for doing Combinator attack. As a consequence, people still used the CPU-based hashcat for serious hash-cracking. This is because it is possible to work with simple dictionary-based attacks.
Fast algorithms like MD4, MD5 or NTLM do work with simple dictionary attacks on a GPU, but this is not very efficient. It takes longer to transfer the wordlist data to GPU global memory rather than to just attack them on the CPU. The reason for this is that they are designed to slow down cracking performance itself. In this case, and unlike the fast algorithms, the time to copy the wordlist to GPU global memory is of no consequence. With this it is possible to do Rule-based attack.
Fast algorithms make use of the GPU-based rule engine to increase GPU utilization. Using this strategy, simple dictionary-based attacks become efficient on the GPU again. The rule-engine on a GPU is very fast. This is an absolutely unique feature against all other hash crackers.