For the first time, folk singers Joan Osborne and Dar Williams are set to join forces performing their own songs as well as each others’ originals. Fans of each others’ work, both artists will round out the performance with a first-time collaborative set. Joan Osborne continues to spread her creative wings long after her 1995 hit “One of Us” gained widespread notoriety, and Dar Williams has more than overcome her early stage fright to become a star of elegiac modern folk. The duo perform together on Friday, Sept. 16, at the Napa Valley Opera House. 1030 Main St., Napa. 8pm. $30–$50. 707.226.7372.