Proof that I'm actually not dead! Had this half done for ages, now it's as done as I care about.
Or, RPGs in general. This post rises from a chat a while ago, and the relative benefits.
To those unfamiliar, the term tank in games is primarily associated with MMOs, and refers to a character with tons of health, armor, or dodge chance who often includes some manner of aggro mechanic to make enemies pay attention to them despite not necessarily being the largest threat.
D&D 4e and 5e add in tank mechanics, allowing such things as granting disadvantage on attacks against other party members, getting free punish attacks if they target anyone else, or such things. Still, the builds that allow such things are often rather specialized, so you MUST build for the tank. You can't have a big generally beefy dude do it, he must use specific weapons and shields and such.
D&D particularly needs such mechanics because every turn allows a full movement and an attack. In theory, attacks of opportunity are supposed to discourage enemies from simply walking around the pointman of the party to conveniently go straight for the squishiest, most not-obviously dangerous party members, but in practice it's darn simple to avoid this, hence why at least some semblance of aggro mechanic options were added.
It got me thinking; What about other systems?
GURPS makes repositioning for attack a lot harder in melee, you have to either spend FP, move and attack as an all-out, or do a wild swing and probably miss. It also features sacrificial parries, and after all out attacks if made to get a proper attack in, the punish that comes after is a massive threat unless the aggressor is very heavily armored. Further, there's rules for blocking enemies from moving past. Defenders can also hold action to get a swing at anyone trying to get past. There's no aggro mechanic in GURPS, but due to the system it's not super necessary.
Shadowrun allows move and attack as well, though they're substantially more restrictive than in D&D. Still, most shadowrun combat happens with boomsticks and cover, rather than melee brawls. Melee fights have the Intercept action, allowing a fighter to prevent someone from moving nearby or pulling back out of melee. Given that the biggest, tankiest people (trolls) have bonus reach in which they can stop people, this makes tanking reasonably doable. There's also a decently large penalty for attacking on the run to try to get around bodyblocking allies.
Deadlands is similar to Shadowrun, but the time period means combat goes to melee a lot more readily. When the highest magazine capacity around save for crazy steampunk portable gatling guns is around 10, they run dry quick vs. hordes of undead and the like. Still, gunfights mean you take cover, and unlike many other systems, Deadlands has extensive rules for staredowns, intimidation, and the like during battle. Running to try to close distance imposes a BIG disadvantage, similar to GURPS and Shadowrun. Other than that, there's not much to stop the badguys from just going around the tanky folks, though.
Savage Worlds, the evolution from the Deadlands system into a simpler, more generically applicable system. In the quickstart, everyone trying to pull back from a melee gets hit by an attack of opportunity, just like D&D. I've currently only got the quickstart rules, but the full book is promised to have a bunch of extra modifiers and special attack types that are no doubt similar to those in Deadlands.