Opera on Tap was founded in New York City in 2005, when a few singers, out for a drink in Brooklyn, wondered what it would be like if classical singers could gig at local bars the way that bands do. Opera on Tap has since grown to boast chapters across the country, one of which is now Colorado. The organization brings opera to unexpected places, offering audiences exceptional music by outstanding singers while giving professional singers the opportunity to perform regularly in public in a welcoming, supportive atmosphere. While casual and even racous, Opera on Tap is not an open mic. Each month’s shows have a theme and singers perform arias and ensembles that more or less match that theme. A performance of “almost all of” Cavallaria Rusticana takes place this evening, September 19 at 7 p.m.; entry is FREE, but you need to click here to reserve. The Academy, 970 Aurora Ave., Boulder. The same program plays again on Saturday, September 26 at 6:30 p.m. at Syntax: Physic Opera, 554 S. Broadway, Denver. Click here for tickets ($8 in advance and students, $10 day of show).