[Lemmy](https://github.com/LemmyNet/lemmy) is similar to sites like [Reddit](https://reddit.com), [Lobste.rs](https://lobste.rs), or [Hacker News](https://news.ycombinator.com/): you subscribe to forums you're interested in, post links and discussions, then vote, and comment on them. Behind the scenes, it is very different; anyone can easily run a server, and all these servers are federated (think email), and connected to the same universe, called the [Fediverse](https://en.wikipedia.org/wiki/Fediverse).