Penny Dreadful: Trauma

From publisher blurb:

Trauma is another small ruleset designed to subject characters to injury and long-lasting effects from combat without ruining their overall experience or penalizing them into uselessness.

Trauma has both a standard, and a 'Hardcore' setting. You can make a choice on how much extra challenge you want added to combat. Trauma works well in dungeon crawls, horror campaigns, and to generally make combat far more frightening without increasing the overall actual challenge rating.