In a mixed commercial and high-tech business park in Kendall Square, Flat Top Johnny's wears its hipster cred on its sleeve. This genuine pool hall (12 tables, no charge) airs alternative rock and metal, chosen by the tattooed and pierced staff. Artwork by local painters hangs on exposed-brick walls; and the felt on the pool tables is crimson, not green. Bartenders tap from one of Cambridge's finest draft beers selections, and that's saying something. Local band members may hang out here when not gigging and rehearsing.