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 compliant with GS. 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.