Sometimes you’ve just got to go with the classics. Sidewalk Cafe’s Monday-night Open Stage is the biggest, best-known, and possibly longest-running open mic in the city. It is open to everyone — musicians, poets, comedians, magicians, er, speed-knitters — who possesses the talent (or self-delusion) to sign up at 7:30 each Monday for an eight-minute set of whatever it is they do. The crowds are notoriously supportive, and the community fostered on Mondays is enough to relax even those who doubt their abilities the most. Famously, this is a place for singer-songwriters to showcase their wares, and many of New York’s now-famous first workshopped their material at Sidewalk, including Regina Spektor, Moldy Peaches, Langhorne Slim, and Nicole Atkins. But the stage is there for all who dare to share.