Facebook recently did a complete redesign of their icon library. I was one of the three designers who had the amazing opportunity to take part in this project. The old icon set were a mix of many different styles since the system was created by different teams as they were needed. The goal of this collaboration was to replace the old set with a new system of 1200+ icons and create guidelines so future designs by their internal team would have design language to follow.
Below is a sample of the icons I had designed in my time with Facebook.