The NRMP (National Resident Matching Program) operates the Main Residency Match. After interviews, applicants submit a Rank order list of programs and programs rank applicants. A matching algorithm then pairs them, and results are released on Match Day.
The NRMP also publishes data on match rates, including for IMGs, which is a useful primary source when you assess how competitive a specialty is. It is separate from ERAS, which handles the application itself.