Your favorite system that goes all-in on a specific thing doing it the best way possible

So I found that the more universally applicable and the more simulationist the system is — the harder it is to make it really excel at anything other than those 2. So lately I've beel more on the lookout for a very specific systems doing their thing the best way possible.

- While PF2E / SF2E is generally praised for it's combat it pales in comparison with something like LANCER, which has a very specific gamemodes and systems that work really only in the intended way and with intended (or close) setting.

- Legend in the Mist has a really fluid and intuitive character building process with great advancements system pushing the narrative forwards it has basically no tactical combat.

- Unknown Armies 3e has really cool magic systems that are overly specific.

- Ars Magica has a set multi-pc-per-player long lasting campaigns (multiple pc generations) where turns may last months full of politics and inventing custom spells.

- Blades in the Dark is really good at making cinematic all-planned heists with little friction and managing a band, but not much more.

So what are your favorite systems for their overly specific thing that they excel at? Maybe it has a really specific power system tied to a setting, maybe the setting itself is that good and unique, maybe it is really a civilization game in disguise, or it is great for playing over text messages, or it is a vtt/videogame exclusive with no table option.