21 Grand is now in its tenth year as Oakland’s foremost presenter of freely improvised music. The Bay Area has the strongest free improv scene outside of Europe, and this noncommercial music simply could not survive without nonprofit art spaces like 21 Grand hosting live concerts. 21 Grand is also the East Bay outpost of the Brutal Sound Effects series (one of the Bay Area’s premier presenters of noise and electronic music), and it is the most frequent venue partner of Club Sandwich, a collective that organizes all-ages concerts with a focus on underground rock. It’s the sort of venue that often features solo performers, but has presented groups as large as a sixty-musician orchestra performing the music of Anthony Braxton in honor of the composer’s sixtieth birthday. At a typical show the audience is in danger of being outnumbered by the musicians onstage, though on the rare occasion that a Sonic Youth side-project plays, the masses cannot be contained within the former warehouse’s walls and spill out into the street. With such diversity of cutting-edge culture, it’s a fine reason to BART over from SF.