Concept 2 SkiErg. See for details on technique. The movement is similar in many ways to rowing, with slightly more emphasis on upper body, but still involves quite a bit of hip opening/closing. Easily exchanged for rowing in any WOD. Once comfortable with the movement and technique, expect top athletes to row about 10% faster than they can SkiErg (a 1:40 500m row might take same athlete about 1:50 to 1:55 on SkiErg for same 500m distance). Good CrossFit Journal Article here:

CrossFit Workshop: Running

Running is a skill and the CrossFit Workshop: Running crew has perfected teaching it. Learn about biomechanics, the science of running, nutrition, injury prevention and programming implementation. Check out the Running Drills series with Brian MacKenzie via The CrossFit Journal: Part 1, Part 2, Part 3, Part 4, Part 5, and Part 6