Last update: 8/15/20
This is a very basic guide on hacking the Wii U. It's meant as a backup in case the ones I linked in the pastebin are unavailable. If you're looking for a more exhaustive guide, try this one.
What can I do with a hacked Wii U?
Running Custom Firmware (CFW) will allow you to do stuff with your Wii U that you wouldn't be able to normally, e.g. play games regardless of region, emulate old games that aren't available on the eShop, dump your Wii U game discs and install them to your hard drive and of course, play games that you did not acquire legally. There's also tons of other kickass homebrew that you can do all kinds of stupid shit with.