Lemon-Lime is the first Gatorade flavor to be produced by inventor Robert Cade and company Stokely-Van Camp, Inc. all the way back in 1965.[1]
Its formula was changed in 1969 to make it more palatable, and to an extension, more marketable for commercial consumption.
It is one of the more common flavors of Gatorade, being available in any store that carries Gatorade. A G2 and ZERO variant of this flavor exist. However, the G2 variant has been made hard to find in recent years, hinting that it could've been discontinued.