What 5e variant/house rules do you play with that work?
I'll be DMing some more 5e soon and I want to take the opportunity to try some different ways of playing (I'll post my own suggestions as comments so they can start their own discussion threads). What alternate rules have you tried that you thought worked well? They can be larger changes to the game or little QoL tweaks (though if you can respond to the suggestion with "at this point just play [different game] instead" then that's probably more than what I'm looking for!)
I have a bunch of houserules in my game, but here are some of my favorite and least complex:
Sprint: If you do not do anything else on your turn and you are not in difficult terrain, you can move up to 5x your speed (150ft typically). Attacks of opportunity against you are made at advantage. This is mainly to allow characters to catch up to combat without waiting 10 rounds.
Fight or Flight: Replaces the frightened condition. You can choose to flee or fight. Fleeing is unambiguous, fighting entails doing everything you can to kill the source of your fear -- no healing, no hiding, no stabilizing, no keeping your smite slots for later. Failing a save by 5 or more forces you to flee. (Taken from an XP to Level 3 video.)
Death saves are rolled in secret.
Light weapon property: we use the OneD&D version.
Critical hits: If you kill a target with one, the damage spills over to an enemy of your choice if I deem it to be within range of that attack. The damage keeps spilling over as long as you kill enemies. For instance, a critical hit with a bow worth 35 points of damage could kill up to five 7HP goblins if they are conga-lining in your direction.
It really gets everyone scrambling to help, and it makes more sense for PCs not to know. It's one of my favorite changes, and it's so simple, it's really good.
Maybe let them know the results if they use their action to make a medicine check to try and stabilise, though tbh the only time I've seen anyone actually do that is at level 1 when nobody's got magical healing yet!
I've run and played in games with no magical healing, and even in games with healers, I find stabilization checks to be relatively common, especially in parties of 2 or 3 where your healer is typically also your front liner (paladin or cleric) and can go down. I don't tend to tell them the number of successes and failures, but I do tell them whether they succeeded or failed in stabilizing and how close their teammate is to death. Something like "while you fail to stop the bleeding, her injuries don't seem life-threatening yet" or "he's still alive, but every breath he draws grows weaker, and you fear the next may be his last". I prefer to stick to natural language when I can.
I do something similar to Sprint, basically, you can move at double your speed for a round (so 4x total, dashing) but have to roll a Con save or take a level of Exhaustion. Each time you use this ability without resting, the DC goes up by 5. (Starts at 10.) Which feels about right, IMO. Lets a max-level Monk/Barbarian match (or exceed, with certain feats/races/subclasses) Usain Bolt for speed, but only for a short duration, even if they have a superhuman constitution.
150ft/round is approx 13.2 sec per 100m which is very achievable for someone who's athletic. I'm not worried about max level barbarians, monks, or tabaxi being significantly faster than is plausible in reality: it's fantasy. Sure, imposing some kind of exhaustion penalty makes sense, but 5e rules for exhaustion are pretty severe, and the point is to not sideline characters who happen to be a bit farther away when combat starts. IMO giving exhaustion would just be another barrier to my players having fun, it would defeat the point of what I'm trying to achieve at my table. But if it works for you, that's great! I'm sure tables that want a crunchier and more realistic game would appreciate your version