Ever heard of Pentatonix? No? Well now you do. They are quite talented people covering famous songs with their voices as their one and only instrument.
It’s the same as the vocal people, which were the ones who made this technique famous worldwide. The main differences are the visuals, they use a theme and have quite interesting disguises, and are fewer.
Here’s one of their best cover (in my opinion).
Pentatonix – Daft Punk Mash-up