Facebook is the largest social media site in the world With more than 2.6 billion monthly active users

Diaspora is a federated social networking service, designed to be a more privacy-aware alternative to Facebook

Gab Social is a fully decentralised open source social network powered by the Gab Platform. 

VK (originally VKontakte) is Europe's largest social network service. It is available in a variety of languages and is particularly popular among Russian-speaking users all over the world.

Friendica is a social network application that is distributed. Which allows users to connect with others through their own Friendica server, but also fully integrates contacts from other platforms.

Hubzilla is a powerful platform for building interconnected websites that includes a decentralised identity, communications, and permissions framework built with standard webserver technology.

Hubzilla

A non-censored social platform where users are incentivized to contribute and curate content.

Used to be called Sgrouples, now its MeWe offered by the company Sgrouples Inc. On its homepage their motto is "The World's Private Communication Network" and "Join the privacy revolution".

Okuna (formerly Openbook) is an open-source, zero tracking, zero spying, zero advertisement, secure social network that gives 30% of it's revenue towards making the world a better place,

Flote is a social network without censorship and vague community guidelines. Here  people can express themselves freely, build communities, and earn digital money.