Microsoft GS Wavetable Synth
Microsoft GS Wavetable Synth (popularly abbreviated as MSGS) is a software synthesizer included with Microsoft Windows since the late 1990's. It is compliant with General MIDI and uses a licensed Roland GS sample set (226 normal instruments + 9 drumkits). The GS standard includes features like reverb and chorus effects[1][2] and tone editing,[2] so despite the name, MSGS is presumably not a GS-compliant synth. The samples are also notably lower in quality than on even the earliest Roland Sound Canvas devices, and the synthesis seems to lack a low-pass filter, unlike the SC series. These characteristics give it a unique sound profile that means works designed for GS devices may not sound good on MSGS, and vice-versa.
The synth does not seem to be documented by Microsoft. Most knowledge about it comes from user testing.