The tape recorder. Ubiquitous in the second half of the 20th century. From spies secretly taping conversations to high schoolers making a mix tape for that special someone, they were everywhere. Not so much now, of course.
If someone should be credited with the invention of the tape recorder, it's Fritz Pfleumer of Austria, whose patent was filed in 1928. American Marvin Camras' innovations came a bit later, but played a big role in its advancement.
Camras started with wire recording and eventually moved to tape. His devices were used by the US Army during World War II (we can only guess if the Germans used Pfleumer's), and paved the way to magnetic storage that followed. Video tapes, for instance.
And while audio and video tapes might be things of the past, Camras was also quite a visionary. Back in 1962, he predicted that by 2012, we would have "memory packs" the size of a box of playing cards that would store gigabytes of sound and video. "Recorded entertainment and information [will] no longer be sold in stores, but [will be] purchased during telephone connections." Sounds familiar?
Camras passed away in 1995, without seeing his vision become reality. At least he missed the death of tape recorders...