The money machine

The money machine is a magical device discovered by the protagonist in Menagerie I: Exoptable Money, which it produces money for him.

The machine can be upgraded via an in-game shop, expanding its functions from only producing bills to coins and topaz, and later cat fur and vital organs. Madame Sinclaire revealed by putting the bodies of cats into a machine, it will produce cat fur, albeit bloodily: spewing out furballs, blood and hair. It is probable Madame Sinclaire used to have another money machine and used it to produce cat fur, alternatively the money machine might be disposed by Sinclaire earlier.

Regardless of how the protagonist may feel after Madame Sinclaire displayed cat fur to him (if he bought a cat early, Sinclaire will even lure it out), the protagonist is later infected with the virus sent by Doctor Money, forcing him to upgrade the money machine to its full extent, including maximizing its capability to create cat fur and vital organs. It implies the protagonist is forced to fully commit to skinning cats and selling organs.

After it is upgraded fully, it continues to produce items for money, until it breaks from overuse.

Trivia
The money machine might be an metaphor on the capacity of earning money.

The protagonist is seen producing money with the machine for no reason. After Madame Sinclaire showed the cat fur, the protagonist still opted to upgrade the machine to produce cat fur, and later selling organs from it. Finally the machine breaks down but then the protagonist is never seen to eat anything.

If the money machine is a depiction of the human body, the protagonist was working and Madame Sinclaire demonstrated how cat skinning could be profitable. The protagonist later was forced to skinning and selling organs, possibly from his body, family members' and relatives' bodies. In the end, it was likely the protagonist's whole family would have died due to virus, the outcome was identical to Madame Sinclaire, which also aligned to how Madame Sinclaire tried to befriend him after showing cat fur, despite showing little remorse on killing his cat and knowing the protagonist would by furious at her.