I'm going to get the ball rolling.
- T'ai chi ch'üan has a technique called "back fist chop", which is usually thought of as a strike to the face with the back of the fist, but can be used, via the back of the forearm, as a collarbone strike.
But it would be hard to do that without significant internal technique, or unless the practitioner is very strong. (Also note that it doesn't work from the outside—the move typically begins from an "embrace ball", where the off-hand has countered a strike or push, and pulls the opponent's arm down while executing the back fist chop.)
- Hsing I Ch'üan has many strikes that can be used to break the collarbone
Including moves that are similar to back fist chop—fast counter, pull/strike with maximum focusing.
Xing Yi Quan is more practical for most practitioners b/c it works pretty well even without a high level of internal technique. (It's sometimes called the easiest and the hardest internal art—easier to use for fighting earlier, but the high-level fa jin typically takes the longest to attain.)
A collarbone break would typically be Pi Quan, which is often described as chopping.
"Pi Quan belongs to Metal... because the movement of the hand is like an ax chopping."
[Trans: Yang Jwing-Ming, Liang Shou-Yu, Xingyiquan Theory, Applications, Fighting Tactics and Spirit ]
It can also be done with a Pao Quan like motion and stance, moving and striking obliquely with the bottom side of the forearm.