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
It’s the first one I always see whenever I look up lists of Fediverse alternatives and I always end up on the site. I use fedidb.org but I don’t use it to find Fediverse software.