Which experimental Apple subsidiary released Harrison's album Electronic Sound?

The experimental Apple subsidiary that released Harrison's album Electronic Sound was Zapple Records.

Founded in 1969 as an offshoot of Apple Records, Zapple was intended for avant-garde music, spoken-word projects, and other unconventional releases. Electronic Sound was one of only two albums issued by the short-lived label; the other was John Lennon and Yoko Ono's Life with the Lions.

Harrison's album was released on 9 May 1969 and contains two extended electronic pieces, “Under the Mersey Wall” and “No Time or Space.” Harrison created them using an early Moog 3-series modular synthesizer, making the record an important experiment in electronic music by a major rock musician.

A common mix-up is Apple Corps, the Beatles' wider company, or Apple Records, its record label. Zapple was the specialized imprint that actually released the album. The label was shut down soon after the album's release, and both original Zapple LPs later became sought-after collector's items.