PixelFed is a photo-oriented social network with filters, comments, likes, shares. As an open source federated alternative to Instagram, it has no ads and no tracking. You can see an example of a PixelFed account here, and an example post here.
The network is made up of lots of independent sites that talk to each other, so you can sign up on any PixelFed site and follow people on the network’s other sites too. (It doesn’t matter if you join a big or small site, they’re all part of the same network.)
Also, because PixelFed sites connect together using the ActivityPub standard, you can follow millions of people on other ActivityPub sites like Mastodon, and they can follow you too.
Unlike Instagram, you don’t need an app to use PixelFed, it works through your browser on phones, computers and tablets. (There are also apps in development for people who prefer them.)