Is the e20 System using the Game System License (GSL) of Dungeons & Dragons 4th edition?
No. The e20 System is not being made under the terms of the GSL, and it is not compatible with D&D 4th edition products (hereafter “4E”). However, 4E, SWSE, and other games that aren’t Open Game Content (Steve Jackson’s GURPS, West End Games’s D6 System, White Wolf’s World of Darkness games, Pinnacle’s Savage Worlds, etc.) can and do provide inspiration for different approaches to the rules, design philosophy, and so forth.