I have already registered with ERAS What is NRMP and do I have to register there
While ERAS and NRMP are both subsidiaries of the American Medical Association, they are separate entities and serve different purposes. ERAS is a vehicle for delivering your application to the program. This is its sole purpose. NRMP is a system that performs matching between programs and applicants. In order to get matched you need both. Again, you need ERAS for submitting your application and NRMP for matching.
Question: There are programs that do not participate in ERAS. How do I apply to them and how do I match with them?
Answer: Indeed, some programs do not participate in ERAS. You have to inquire these programs directly about specific ways of submitting your application there. However, you should be aware that typically these are special programs that most likely you wouldn’t qualify for anyway, like military programs reserved for medical school students whose education was paid for by the Army.
Question: How do I find what programs do not participate in ERAS?
Answer: You can use FREIDA online search  Under Optional Criteria select “Do Not Participate in ERAS”
Question: Do all programs participate in NRMP match?
Answer: No. Some programs offer all their positions directly without waiting for the match. You can find these programs on FREIDA:  Under Optional Criteria select 'Do Not Participate in NRMP'