The Massachusetts Museum of Contemporary Art is known for its musical events, and the FreshGrass festival is among the highlights, showcasing dozens of bluegrass artists and bands on four stages over three days. This year, the lineup includes Shakey Graves, Molly Tuttle & Golden Highway, the Devil Makes Three, Drive-By Truckers, Béla Fleck, Edmar Castañeda, Antonio Sanchez Trio, Steel Pulse, and more.