#Lemmy is an open federated alternative to Reddit and is currently early in development. You can follow the project at:
There's also the open federated #Prismo, which is in a more advanced state of development:
You can try Prismo at:
(If you copy a Prismo user or post address into the Mastodon search box and click search, you can interact with it.)
(Thanks to @gaja for info about Lemmy.)
mastodon.at is a microblogging site that federates with most instances on the Fediverse.