“In Celebration of Alex Cooley” brought together several thousand Cooley friends and fans for two hours of live performances and a look back at a remarkable career that began when the 29-year-old music neophyte decided to stage the first Atlanta Pop Festival in 1969 in Hampton, of all places — and Janis Joplin, Led Zeppelin and some 150,000 patrons all showed up. The Indigo Girls, Kristian Bush, Blackberry Smoke and Drivin' N Cryin' all performed during the evening.