If you are using a DOS operating system (MS-DOS, PC DOS, DR-DOS, FreeDOS), there are a number of CP/M-86 emulators for DOS. These emulators also work within DOSBox.
If you are using any other operating system, you can install CP/M-86 in an emulation or virtualization program. Such programs allow you to run CP/M-86 and other operating systems as a "guest" operating system in a window on your "host" operating system. You can also run a CP/M-86 emulator from within a copy of DOS running within an emulator or virtualization program, or from within DOSBox.
CP/M-86 continued the legacy of CP/M on the x86 platform. Version 1.1 introduced support for hard drives. It was followed up by CP/M-86 Plus and Personal CP/M-86.
Lineo, Inc. graciously declared CP/M-86 freeware on 19 October 2001.
DOSBox emulates a complete IBM-compatible PC, including almost every significant graphics standard (CGA, EGA, VGA, etc.) and sound card (Sound Blaster, AdLib, Gravis UltraSound, etc.). DOSBox also allows the emulation speed to be decreased to allow very old software to run at a playable speed. What makes DOSBox unique is that it also emulates DOS itself, allowing DOS software to run without installing an actual copy of DOS! DOSBox emulates DOS so well that it is even possible to install Windows 3.1, as well as Windows 95 up to OSR1. It is also possible to install and boot an actual copy of DOS in order to use utilities not included with DOSBox, or just to recreate the authentic DOS experience. In additions to the versions listed below, there are also ports to a number of Linux distributions, so I recommend visiting DOSBox's home page if the version for your operating system isn't listed below.
PCem is a PC emulator that lets you configure pretty much everything about the emulation. Besides the usual ability to choose a graphics card and sound card, you can pick a specific CPU and clock speed to emulate (i.e. 486 SX 33). The emulation is very accurate, but one of the reasons why it's so accurate is that PCem requires the actual ROMs of the hardware that it emulates (fortunately, most of the software that you need is available on the PCem website). This means that you can actually enter the CMOS Setup! PCem pretty much recreates the entire PC experience, and even emulates the PCjr.
Virtual PC allows almost any PC operating system to be run in Windows with virtually no loss of performance. You can run a real copy of DOS, OS/2, or Windows as a "Guest" operating system within your normal version of Windows (the "Host" operating system). Virtual PC is a virtualization environment, not an operating system emulator, so you will have to install your own copy of whatever OS you want to run as a Guest.
Virtual PC 2004 requires at least Windows 2000, and supports DOS, OS/2, and Windows 3.x (unofficially)/NT/9x/2000/XP/Server 2003 as Guests.
Virtual PC 2007 requires at least Windows XP, and adds support for 32-bit Windows Vista/Server 2008 Guests. Official support for DOS and Windows NT/95/98 First Edition/Me Guests was dropped, though they still work just fine.
The newest version, released on 19 September 2009, is called Windows Virtual PC. It requires Windows 7 and only supports Windows XP/Vista/7 Guests, so it is not useful for running any of the games on this site.
Microsoft generously released Virtual PC 2004 as freeware on 12 July 2006. Virtual PC 2007 was originally released under a freeware license.
22DISK is the single most important utility in the history of retro computer archiving. At last count, 22DISK can read and transfer files to and from 8", 5.25" and 3.5" CP/M disks in 187 formats. Support formats include some of the most important 8-bit computers ever created, such as the Coleco ADAM, DEC Rainbow, Kaypro, Osborne 1, and TRS-80, as well as 16-bit IBM PCs running CP/M-86. 22DISK users created disk definitions for almost every format that 22DISK didn't natively support. 22DISK is one of a number of indispensible tools created by Sydex.