In terms of education, credentials, salary, responsibilities, places of work, basically all the little details that differentiate the three.
A physical therapist (USA) and a physiotherapist (rest of the world) is the same thing. They are skilled professional that perform a wide variety of techniques to "rehab" an injury, birth defect, etc. Patients are from birth to geriatric and all organ systems. In the US, PT is a graduate degree and ATC is still mostly a BS degree. ATC provide on field coverage for sports injuries and rehab back to the field. They treat only a very small portion of the poplulation for a very specific function.