SPOILER WARNING: This article contains major spoilers for "Midvale," the latest episode of Supergirl.
In "Midvale," the latest episode of Supergirl, Kara made a direct reference to Smallville continuity. As the adolescent versions of Alex and Kara investigated the death of Kara's friend Kenny, Kara sought help from one of Clark's friends: Chloe.
While this seemed to be a passing reference to longtime Smallville character Chloe Sullivan, one of Clark's close friends on the earlier series, Kara made the mention all that more explicit when she brought up Chloe's "Wall of Weird." In Smallville, Chloe was a budding reporter who followed all of the strange occurrences that happened in their small town; she kept track of them all by posting tabloid clippings to a cork board, which she dubbed her "Wall of Weird." By referencing the Wall of Weird in the same breath as Clark's friend Chloe, Supergirl seemed to anchor a little bit of Smallville's world in the Arrowverse.
Supergirl didn't stop at the mere mention of Chloe. Though she never showed up in person, Chloe offered Kara a helping hand with some of her tech prowess. Kara had uncovered Kenny's laptop, which had a handful of encrypted files on them. Since she couldn't unlock them herself, Kara sent the files to Chloe, who decrypted them as a favor. The decrypted files gave Kara and Alex the tools they needed to track down Kenny's killer: a crooked cop who Kenny had caught red-handed.
Of course, in Smallville, Chloe was something of a tech genius. When her career as a journalist tanked, she became a full-time ally for Clark "The Blur" Kent and Oliver Queen's Green Arrow. She even got a nickname of her own: Watchtower. Though she was always tech savvy, Chloe developed near-metahuman skill with technology after she was possessed (and nearly killed) by Brianiac. As such, Chloe's tech skills tie her back to Smallville continuity.
Since Chloe was created specifically for Smallville, she has no real analogue in the comics. She did turn up for a few issues of Action Comics, though the comic book version of the character never quite took off the same way.
Airing Mondays at 8 p.m. ET/PT on The CW, Supergirl stars Melissa Benoist as the Girl of Steel, David Harewood as Martian Manhunter, Mehcad Brooks as Jimmy Olsen, Chyler Leigh as Alex Danvers and Jeremy Jordan as Winn Schott, with appearances by Calista Flockhart as Cat Grant and Tyler Hoechlin as Superman.