Cheap$kate -- Free things in NYC this week

Lady Gaga launches three-day ‘ARTPOP Pop Up: A Lady Gaga Gallery’
Gaga’s ARTPOP could mean anything, so come make meaning of it for yourself. The Grammy winner is showcasing a special three-day exhibit in conjunction with the release of her latest album, “ARTPOP,” in stores today. Starting today through Wednesday, check out the ARTPOP Pop Up, which will feature props and outfits from the pop sensation, along with interactive experiences. (Monday-Wednesday, noon-9 p.m., FREE, 417 W. 14th St., ladygaga.com/news)

Open Mic Night at GTR Store Showroom
As a celebration of its new showroom, the GTR Store is launching a weekly Open Mic Night every Monday and Tuesday, starting tonight. The cool stylings of jazz musicians will fill the air on Monday evenings, and the tones of acoustic sets will permeate Tuesdays. So come out and hear local musicians tout their musical skills. (Mondays & Tuesdays, 5-9 p.m., FREE, GTR Store Showroom, 141 W. 28th St., fourth fl., gtrstore.com/showroom)

Inside MAD: The ‘Usual Gang of Idiots’ pick their favorite MAD spoofs
It’ll be pure MAD-ness at Barnes & Noble Upper East Side tomorrow evening as MAD magazine editor-in-chief John Ficarra gets together with Al Jaffee, Desmond Devlin, Tim Carvell and Sam Viviano to discuss the editors’, writers’ and artists’ all-time favorite MAD articles. Stop by to hear the discussion of their most beloved gags, satires and spoofs, as well as chat about the celebrity essays — from the likes of Roseanne Barr and Ken Burns — in the book. (Tuesday, 7 p.m., FREE, B&N Upper East Side, 150 E. 86th St., 212-369-2180, bn.com)