Remembrance tanks were a technological means of reproduction, which converted biomass into people based on arbitrary specifications, comparable to the Great Houses' breeding engines. They were primarily used by the Remote and to produce Remakes.
Faction Paradox created the Remote as a media-orientated culture, and designed their reproductive system to match. The Faction claimed that the tanks "might be useful in an emergency." In fact, they deliberately mass-sterilised the Remote, leaving remembrance tanks their only option for long-term survival. Every time an individual died, their friends and acquaintances would pour their memories of the person into a tank, which used the memories to sculpt a new iteration of the person from raw biomass. This meant that there was no difference between each person's inner self and their public perception, and that with every death they became slightly more exaggerated or stereotypical. In the same way that even standard human cultures were shaped by their media, and the Remote were shaped by their signals on even a biodata level, the remembrance tanks meant that every one of the Remote was biologically a product of their culture. (PROSE: Interference - Book Two, Remembrance Tanks)
In the City of the Saved, remembrance tanks were naturally not needed to sustain population. Instead, they were used to make Remakes, recreations of fictional characters (and occasionally religious figures). The largest group were Remakes of Sherlock Holmes, which operated the Great Detective Agency. (PROSE: Of the City of the Saved...)