PCSX2. It’s an open-source PS2 emulator, and a dang good one at that. It has a high degree of compatibility and functionality. I absolutely adore it since so many of my favorite games happen to be PS2 games, and after playing some of my favorite games on this emulator, I realized just how much the PS2’s native resolution doesn’t do the graphics of the PS2’s best games justice.
It is also free and available for Windows, Linux, and macOS!