There are 4 thing that come to my mind. But they are all pretty different and depending on your build no the only source of damage.
Things are: Aura Of Decay (Acolyte/Lich), Death Seal Also Acolyte/Lich, with Death Wave occuring frequently specced), Maelstrom (Primalist/Shaman) and Fire Aura (Mage, best supported by Spellblade)
Some details about those things:
Aura Of Decay: Stacks poison on enemies inside it very quickly, but also poisons yourself, but you take decreased damage from poison while it’s active. Needs some ivnestment to make it work smoothly, since it damages you. So you need alot of sustain(there is selfhealing insdies AoD’s skill tree, which is highly recommended if you don’t have much other ways of sustaining early.
Death Seal: Baseline the skill only releases one wave of death at the end. But you can spec into Waves Of Death spawning frequently whiel the skill is active. This does not have 100% uptime, since the skill has 5 sec cooldown and a limited duration(5-8 seconds, depending on how you spec if i remember correctly)
Aura Of Decay and Death Seal can be combined if you want
Maelstrom: By default it’s a cast with a small casting animation, but you can stack it, it has no cooldown and gives you an ever increasingly area of cold damage around you. There are ways to give you stacks via other means (On Kill via Skill Tree, Idols can cast it every x seconds and Passive Tree chance when hit). This is a very active playstyle since you need to keep the stacks up and running. There is also a node which makes it instant cast, but gives it a cooldown, which makes it play more fluid, but you are very reliant on all the other sources to get high stacks
Fira Aura: It’s not an active skill actually, but a buff that stacks, At one stack an aura aroudn you appears that deals fire damage by default. The more stacks you have the more dmg it does. There are Ways to alter the base dmg and abse stast via passive tree or active skill trees of other skills. Spellblade Mastery has a whole Passive Tree Section revolving around this. Making it viable as Fire, Lightning or Cold.
Except Aura Of Decay, all of those are more or less active playstyles and not so much “passive”.