Finger augmentation devices, those that are worn and operated by fingers, are a rapidly growing field in the human--computer interaction domain. This field is rooted in ancient history; however, still the academic research arena is booming with new finger augmentations every year. This article strives to survey the entire body of work on finger augmentation devices and uncover the trends and the underexplored territories. We contribute a methodical classification of over 150 pieces of academic, product, patent, and concept work. We discuss the underlying sensing and feedback modalities and provide a definition, taxonomy, and reference for researchers of finger augmentation devices.