In their heyday it looked like this:

New York Public Library

Today it’s like this: an air plant cabinet.

Re-purposing card catalogs is nothing new but it is still hot.  Apartment Therapy recently did a post on card catalog furniture like this dining room buffet:

Never fear libraries are re-purposing them too, this is an ereader charging station Publisher’s Weekly wrote about:

The Providence Athenaeum still has it’s wonderful, antique card catalog with it’s 19th century hand written cards on prominent display but the other day our custodian removed a not so old, not so beautiful, card catalog from the Children’s Library for offsite storage and before he could get it into the truck he received a proposition to purchase it!