I've been working on a randomiser for Minecraft Java Edition for the past few days, and have finally completed it. This tool randomises Minecraft's assets (textures, models, sounds and text). It's designed for Windows, but you should be able to run it on Mac OS and Linux if you install the Mono Framework (I'm not sure how to use the Mono Framework though, I've only read about it online, and can't test it myself).
Minecraft Randomiser allows you to select the Minecraft Version you want to randomise, and has a seed option. This is compatible with Minecraft Java Edition 1.8 and newer. It randomises the jar file's assets and outputs a resourcepack titled something like Random-1.13-20190421122141. You can consider this a challenge, since you have no idea what is what.
I recommend randomising the Block Models, Item Models, All In-Game Text and Sounds. I DO NOT RECOMMEND Other Textures, because the game crashes. It can truly make Minecraft challenging (if you don't use F3 of course). The seed used for the screenshots is the one in the screenshot below.
Screenshots:
Screenshots from Minecraft:
