Chinese internal martial arts: Tai Chi, Xingyi, and Bagua. The word "chi" does not carve reality at the joints: There is no literal bodily fluid system parallel to blood and lymph. But I can make training partners lightheaded with a quick succession of strikes to Ren Ying (ST9) then Chi Ze (LU5); I can send someone stumbling backward with some fairly light pushes; after 30-60 seconds of sparring to develop a rapport I can take an unwary opponent's balance without physical contact.
Each of these skills fit more naturally under different categories, but if you want to learn them all the most efficient way is to study a Chinese internal martial art or something similar.
I used to go to a Tai Chi class (I stopped only because I decided I'd taken it as far as I was going to), and the instructor, who never talked about "chi" as anything more than a metaphor or a useful visualisation, said this about the internal arts:
In the old days (that would be pre-revolutionary China) you wouldn't practice just Tai Chi, or begin with Tai Chi. Tai Chi was the equivalent of postgraduate study in the martial arts. You would start out by learning two or three "hard", "external" styles. Then, having reached black...
The title says it all.