Both anime pull legendary heroes (Fate takes those from world history and lore while Re:Creaters takes those from otaku media) from other worlds into one and seemingly duke it out with each other.
Heroes from legend are brought into modern day and meet up. Fate is a large series with many heroes looking back at their legends, Zero is the better part to be animated so far. Re Creators takes some fictional characters it made up and has them meet their creators and meet other genres.
Same director, grand magical battles in the real world with complicated magical mechanics. There is no plot armor, there is a large cast and people will die!
Both have a dark plot but in fate zero they summon heroic spirits called servants and in Re:Creators anime character are summoned
Both of these series have the same director and they are both anime where powerful figures appear in the real world and fight each other. Fate Zero involves historical figures fighting for the Holy Grail while Re:Creators involves characters from various forms of popular media (anime/light novels/video games) fighting over the fate of the consumer world and the people who created them.
Re:Creators is directed by the same director as Fate/Zero, that being of Ei Aoki. His work continues to be phenomenal in this series, with his assistant director being that of Rei Hiroe, another amazing director. Though these 2 series are almost nothing a like, you'll enjoy the quality of Re:Creators because of Aoki's amazing direction.
How is this similar, you say? Okay, I have two solid points
First, it has the same battle royale thing going on with participants came from alternate reality.
Second, both of the series deal with a really heavy dialogue (or character drama, as some people say) to move the plot along with the action
As why I pick Fate/Zero over Fate/Stay night for the similarity lies in the visual as well, both are equally stunning in my eyes and both keep me on the edge of my seat until the end
The characters are summoned and destined to fight each other. Each characters has a human to protect. Action packed.
Both are battle-royale type series with characters of different backgrounds. Fate zero is a bit darker while ReCreators is more of a reverse-isekai
Both revolve around the idea of powerful well known* characters that don't really belong in the modern world ending up in it. That then end up clashing due to a difference in ideals and goals.
*Re:Creators only contain original character so they are only "well known" in universe
F/Z has servants summoned by masters and ReCreators has a similar type of concept but the heroes unintentionally appears and originates from creators (e.g. manga writers in that anime's universe). Both have excellent build-ups and conclusions are sad to see knowing that you wont find another masterpiece in a similar niche as these two. Definitely worth rewatching and both have great OSTs which, depending on how much you're into the anime, can give you the "FEELS" factor.
Both starts a bit slow and have some edgy shit happens now and then