Miiverse is described as 'Service that lets you communicate with other players from around the world. It is accessible via Wii U and systems in the Nintendo 3DS family' and is a Social Network in the games category. There are 2 games similar to Miiverse for Web-based. The best Miiverse alternative is Closedverse, which is both free and Open Source.
An open-source spinoff of Openverse programmed in Python and Django. Closedverse resembles the browser version of Miiverse and has extra features such as image / video posting, a dark theme, built-in drawings + messages, custom profile pictures, and other things.
grape is a Miiverse clone written in PHP by Arian Kordi featuring features a Wii U (portal) interface as well as a browser (offdevice) interface and an unfinished n3ds interface. It shares some internal elements with Miiverse.
