Lemmy is a link-aggregator and the Fediverse's replacement for Reddit.

File:Lemmy logo.png
Lemmy logo

Website join-lemmy.org
Official instance lemmy.ml
Instances list /instances

What does Lemmy feel like?

Lemmy is similar to sites like Reddit, Lobste.rs or Hacker News: You subscribe to communities that you're interested in, post links and discussions and vote and comment on them.

Further Reading

How do I get an account?
Getting started with your Fediverse account
Mobile apps
Best practices
Lemmy - the advanced page on Lemmy