One thing that annoyed me about moving to Lemmy was that I’d lose my subreddits and that looking for and joining communities on Lemmy would be tedious. So (logically) I spent 2 days writing a script, that gets a list of your subreddits from your reddit account and looks for communities with the same name on Lemmy. It also joins those communites. So all you have to do is download, enter your credentials and you’re done.
It tries to subscribe to the one on lemmy.world as well as the most subscribed one on any instance according to lemmy.world.