Now in its 15th year, Acorn Productions’ Maine Playwrights Festival always delivers satisfying surprises. Among the six new works being presented at St. Lawrence Arts (76 Congress St., Portland) this year are three that tackle thorny issues in the Middle East, two romantic comedies, and a play about gender identity in 19th century New Hampshire (also a thorny issue, to be sure). Tonight’s performances start at 7:30 p.m. Tix: $16 ($14 students and seniors). 347-7177. Full schedule at acorn-productions.org.