Commercial Social Networks are accessed either through their own app, or a web page. In either case they exist as an island, although a giant one, accessible only to its inhabitants. If you want to visit these, beyond a teaser glimpse, you have to create an account, allowing them to claim large population and influence, and data to sell to the advertisers who fund them.
There are also a large number of much smaller islands, which welcome visitors. You do not need to provide any form of identification – such as creating an account to look around, though you will need an account somewhere on this network of sovereign areas to follow or comment. This collection of sites is also known as the Fediverse.
Examples
Here are a random selection – well not really random – there is quite a lot of technical and bits on the Fediverse, written by technical people for other technical people, so these are less usual, but growing in number.
https://mastodonapp.uk/@uktw – UK Theatre Web
https://mastodon.social/@gutenberg_org – Project Gutenberg – if you are into books, so are they.
https://mastodon.scot/@scotlit – Association for Scottish Literature – -if you are into Scottish Books
https://mastodon.social/@onlmaps – interesting maps
https://mastodon.social/@medieval_illuminations – Medieval Illumination