These are the best SEGA Master System and Game Gear (and other consoles) emulators available. They differ in what they offer but they will all get you playing your favourite classic games well.
Emulators for Windows (and even DOS) have been progressing for years. Recently there is more of a shift in bringing these programs to other platforms such as PSP, I-pod, GP32 and even the Saturn.
Many of these programs will also emulate SEGA's older consoles SG-1000, SG-1000 Mark II, SC-3000, SF7000.
Each emulator differs slightly in their performance but as a basic rule you can get full speed play under Windows XP with a Pentium 3 class CPU running at about 600Mhz. Running Windows 98 you can probably get away with less.
To download the emulators, right click the links and select Save Target As... to save the file to your hard drive. All files are zipped so you will need to extract them.
Be sure to have the latest version of DirectX installed on your system for the Windows versions. You can get it from here.
Any homepages for the emulators are included if they are still online.
MEKA 0.73
Requires Windows (Not NT) and Direct X.
DOS and Linux versions available
Meka is one of the older emulators around and thus is highly accurate and has tones of features. These include support for the light phaser, 3d glasses, debugging, sound logging and program themes.
The Windows version does require a slightly powerful machine to run with all the features compared to Dega.
The name Meka is from the Dragon in [Wonderboy] which just happens to be one of my most favourite games of all time! An excellent emulator.
Homepage: http://www.smspower.org/meka/
DEGA 1.12
Requires Windows (not NT) and Direct X
Dega is rock solid stable with an excellent performance and high compatibility level. It has a nice simple interface to use and has some cool features like logging the audio, enhancing the PSG audio of the system, grabbing screenshots and importing save states from Meka.
Homepage:http://www.finalburn.com/dega/
This emulator has also been ported to Linux.
KEGA Fusion 3.64
Requires Windows (not NT) and Direct X
Not just a Mega Drive/Mega CD/32X emulator it also emulates Master System, Game Gear and Pico.
Emulation is of high quality and accuracy and has lots of features such as net-play and video recording.
Homepage: http://www.eidolons-inn.net/tiki-index.php?page=Kega
BrSMS 1.21r
DOS
This is a fairly complete Master System and Game Gear emulator and was considered the best at one point. It runs mega fast even on a 486 since it's written in assembly.
Being DOS and fairly old there is not really a GUI so new users may find this difficult to use but if you have a slow PC this is the way to go.
Work on this emulator was discontinued a few years ago.
Other Operating Systems
Some of the emulators above have ports for Linux. There also exists emulators for Mac OS as well. Master Gear is another emulator and is available for both Linux and Mac OS.
SMS+ is a port of a PC emulator and can be obtained from here http://www.bannister.org/software/sms.htm
BIOS Files
Some of these emulators can make use of the Master System and Game Gear BIOS images for improved emulation. Refer to the readme file with each emulator on how to make use of them.