A good old-fashioned talent show is the gold standard of community music projects. But to make it truly a "project," it would have to have an important theme either locally or globally. This will garner more commitment and attendance in support of something rather than to just ask people to attend.
A sing-along may sound a bit unexciting, but imagine if an entire community got together for food and fun. Random songs of a pre-determined genre or style would play through loudspeakers, and people would be infected to sing. It can be made a fundraiser or be designed so that certain groups of random people have to sing along to certain songs and then compete in a brief competition for prizes.
Collecting the community together to watch a musician or band perform is the one thing that is already being done exponentially. But if it is done as a benefit or a memorial, it becomes a different type of event, one that a community would be more apt to attend. If there is a band that is from the town, it could be a great venue to build up community pride.
A community day of music with everyone grabbing an instrument or using their voices in random spots of town would be a great deal of fun. Imagine if everyone with any type of musical ability all went into the town center and found a spot to perform at the exact same moment. Each would perform whatever pieces they wanted, while the other members of the community would walk through town enjoying the human radio station.