This year Popcorn Anti-Theater brings the first-ever stageless play to the Fringe; audiences board the group's Mexican Bus and ride across the city to see skits in different neighborhoods. More conventional shows like Moog Bandits Gave Me the Clap ("apocalyptic Queer-o-vision" comedy) and Bardo "A" Go Go (Tibetan shamanic theater) alternate for 10 days among five downtown theaters: Tickets, like theater space, are sold on a first-come, first-served basis 30 minutes before each show; ticket prices never exceed $8. The festival's opening night party begins at 11:30 p.m. Thursday at the Exit Theater, 156 Eddy, S.F. Admission is free. Shows run Monday through Friday at 7, 8:30, and 10 p.m., and Saturday and Sunday at 1, 2:30, 4, 5:30, 7, 8:30, and 10 p.m. through September 19 at the following venues: Exit Theater and Exit Stage Left (156 Eddy), Shelton Theater (533 Sutter, lower level), Il Teatro 450 (449 Powell, third floor), Lorraine Hansberry Theater (620 Sutter), and the Mexican Bus -- viewers board outside the Exit Theater. For a complete schedule and description of shows, call 673-3847 or visit the festival's Web site at www.sffringe.org.