I've been following lemmy [0] for a while, a federated reddit alternative in the same spirit as mastodon. It's still very small, but I think as monetization pressure on reddit increases, people will look for other places to post and this might be one of them :)
Their website mentions the Fediverse. lemmy is a federated network that is completely separate from the mastodon/diaspora/... network, right?
Since I already have an account on a mastodon instance I first thought I can just connect to lemmy instances using that but that is apparently not possible.
Yes, you can. After their last release you can follow Lemmy communities with Mastodon and add comments to posts. Just enter the URL of a Lemmy community in your search bar to find the account profile. And in case that doesn't work you might try search for @[CommunityName]@[lemmy.instance] (there are some issues to be wrinkled out still).
edit: add the link [0] https://join-lemmy.org/