ATHLEAN-X is a company lead by Jeff Cavaliere dedicated to provide training programs. He has a master degree in physical therapy. On the official site, you can find programs for a fee as food supplement. On the Youtube channel, you can find many videos including for:
- improving your posture
- improving strenght of specific muscles with either bodyweight or some equipment (e.g. barbells, dumbbells, elastic bands, etc)
Jeff Caveliere gives valuable tips on how to avoid bad movement, do good movement with explanation on how our body works (role of muscles, bio-mechanics, etc.).
However, if you want to do only body weight exercises without taking any food supplement, then some videos may be less helpful. The focus of the videos are also more on building strength, some on explosivity and less mobility as for example on GMB Fitness and use more often weight compared to Calisthenic Movement. There seems to be no use of rings. Some suggested training sessions are also quite intensive.
As a conclusion, even if you are doing only body weight exercises, ATHLEAN-X is a valuable source information with the wealth of information for free on the official Youtube channel and Jeff Cavaliere has a good expertise in body training. Even for people that are not dedicating much time on sport, some videos may be useful (e.g. how to improve posture).