One fav=one upvote afaik. I’m not sure how downvotes work.

The biggest difference is if it’s group or individual-oriented. Lemmy does the post to group thing. Friendica’s group function does the group thing. Friendica also does single actor posts, like Mastodon and the micro bloggers. I’m not sure how they’ve solved the lemmy to mastodon thing, but it was initially not federating because Mastodon didn’t support the group function, or lemmy didn’t support the single actor posts - either or.