Roland GS stands for General Standard and is a proprietary extension to the MIDI standard. It adds 98 tonal instruments, 15 drum and percussion instruments, 8 drum kits, plus reverb, chorus, and variation effects.
The first synthesizer to support Roland GS was the SC-55 SoundCanvas, released in 1991.
Yamaha XG was created to compete with GS.
This is a partial list of hardware that supports Roland GS.
GS is no longer widely marketed, used, or supported. This is mainly due to the creation of General Midi 2, which actually includes GS compatibility.