ACT. Not long after its founding in the mid-1960s, the city's major nonprofit theater company became one of the nation's leading regional theaters. During its season, which runs from early fall to late spring, ACT presents approximately eight plays, from classics to contemporary works, often in rotating repertory. In December ACT stages a much-loved version of Charles Dickens's A Christmas Carol. The ACT ticket office (405 Geary St., PHONE: 415/749-2228) is next door to Geary Theater, the company's home.