In addition to hardware support, the Yamaha XG standard was also implemented in software. Most XG software only supports Windows 95 a, 98, and ME since those were the most popular operating systems during its time.
Yamaha released a few versions of their XG softsynth. Here are the differences among variants in the S-YXG series:
A general MIDI software synthesizer that lacks XG support. It was only available in Japan. Windows 9x only.
Supports General MIDI and the XG Lite sound set. Windows 9x only.
Supports General MIDI and the full XG sound set consisting of 676 voices and 30 drum kits. It also included 11 chorus, 11 reverb, and 43 variation effects and required 32MB of RAM and a 166 MHz processor to run. It was bundled with some video games and sound cards. Windows 9x only.
There was a trial version of S-YXG50 offered, and it is available for download here (9MB). It is not possible to buy a registered version.
A WDM version of S-YXG50 that works on Windows NT, 2000, and XP.
A VST instrument version of S-YXG50 bundled with digital audio workstation software (SOL2) and only available in Japan.
This combines the XG20 and XG70 into a single program. It was not available directly, but was bundled with a few games, including Final Fantasy VII for PC. Windows 9x only.
This included General MIDI, the full XG sound set, and one voice of virtual synthesis. Windows 9x only.
This included General MIDI, the full XG sound set, and eight voices of virtual acoustic synthesis. It was only available in Japan. Windows 9x only.
This is a DirectMusic version that shipped with Final Fantasy 8. Windows 9x only.
A newer XGLite version with no GUI.
Japanese versions of S-YXG50 and S-YXG100 also supported vocal "formant synging" synthesis like that available in the PLG100-SG Yamaha expansion board. That later evolved into the Vocaloid voice synthesizer.