Wikipedia
RealPC was a Macintosh program that emulates an x86 PC, allowing the use of MS-DOS, Windows NT, Windows 95, and Windows 98. RealPC was compatible with PowerPC macs running system software 7.1.2 through 9.2. Requirements were: Any Power Macintosh or Mac OS compatible, System 7.1.2 or later, Minimum 16 Mbytes of Ram, hard drive space for 50 Mbytes (MS-DOS), 60 Mbytes (Windows 3.x), 130 Mbytes (Windows 95), and any Macintosh compatible CD-ROM drive. RealPC emulated a Pentium-based PC with MMX technology, supported Sound Blaster and MMX, and allowed you to use a Macintosh joystick, allowing you to run PC programs, including MS-DOS, and Windows, games and applications, alongside your existing Macintosh applications. RealPC was provided with MS-DOS 6.22 already installed, so you could immediately run MS-DOS games and applications on your Macintosh. Linux was not supported and due to shared RAM between MAC-OS and RealPC Windows-98 was the reasonable limit. RealPC was able to convert Virtual-PC hard disk files to use and run the installed OS.
RealPC was discontinued in 2003.