If you still have your original Wii console sitting under the TV, this is the most authentic way. Nintendo no longer supports Wii Shop Channel or online services, which means modifying your console is now incredibly safe and legal (as long as you dump your own game discs).

Only for experienced Wii homebrew users who understand the risks. Beginners should stick to legal options like used discs or the Wii U eShop (while it lasts). If you use this site, always scan files and keep your Wii offline afterward.