pretendo.network
Pretendo Network is a free and open source replacement for Nintendo's servers for the 3DS and Wii U, built through clean-room reverse engineering. It aims to preserve online functionality for those consoles, and Cemu 2.1 officially supports it under network account options. Connecting on consoles requires hacks such as Aroma for Wii U and Luma3DS for 3DS, though Wii U also has a limited hackless SSSL method.