No idea if they still do but Slashdot used this back in the day. You were given karma points occasionally to pass out and you'd have to select what you were rewarding/punishing.
To this day, I prefer Slashdot's summaries over headline-only aggregators, and I wish other sites would adopt features like the mod-with-reason and karma caps per comment. But they designed the system to limit the power of moderators, and those limits didn't scale with the imbalance between trolls and good-faith posters
Considering the amount of fuckery people engaged on during the site's heyday its moderation system handled things amazingly well. If you read at a threshold of +1 you'd barely see all the garbage posted there.