PS21: Performance Spaces for the 21st Century, Columbia County’s summer arts fest, offers everything from live theater to films, jazz concerts to community sings. This season, dance takes center stage, as the inaugural Chatham Dance Festival gets underway in August. July’s highlights include ventriloquist Steve Charney and his chum “Harry” (July 18), a concert of music by 17th-century composer Henry Purcell (July 19-20), and the Actors’ Ensemble production of two short plays about life on the prairie at the turn of the 20th century (July 25-26). Performances continue through Sept. 6. Call or visit Web site for complete schedule and ticket information.