SHA-256 was quite similar to SHA-1 in many ways, and much of the code used to implement SHA-1 was borrowed. The project is hosted here. I also implemented SHA-512, which is hosted here.
Blockchains have always been on my mind, so perhaps I will implement a little blockchain next. My purpose in doing these little projects have been to understand how these ubiquitous yet esoteric technologies work under the hood. I never feel satisifed solely using a library; I feel like I know what I am doing if I can recreate a library.