jointhefediverse.net seems to be a commonly linked resource for directing people to join the Fediverse.
Curiously, it does not list Lemmy under the list of Reddit alternatives. Their GitHub README explains why.
Previous relevant discussion: https://lemmy.ml/post/78808
They keep changing every few weeks, so I guess that’s why people haven’t summarized the differences.
Do you have any question in particular?
I see. No, I don’t think I have any specific questions at this point.
There’s also https://piefed.social/ that is promising