Перо́ is used for a bit different kind of pen:
The main meaning of «перо́» is feather, hence it's also used for quill pen. But it's not something we would use for writing nowadays.
Oh, that's cool!
Actually, перо is also used for the 'nib of the fountain pen' (but I've never heard it used for the whole pen, only for a part of it):
Also, I think перо is some tool used for drawing, but I'm not sure how it's used exactly. Here's a перо for drawing sold in a shop: http://www.kancelarka.com.ua/tovar/15863/ (is it put in a pen? or just used as is? no idea)