Free icons
Handy when you design sites, apps, etc. All three offer SVGs so they scale up nicely in modern screens with ridiculous resolutions.
- https://thenounproject.com/ - you need to give credit to the author
- https://www.zondicons.com/ - couldn't find terms of use, says Creative Commons at the bottom, but not sure which. I'm sure giving credit would be nice.
- https://fontawesome.com/ - Creative Commons 4.0 license which means "You must give appropriate credit, provide a link to the license, and indicate if changes were made."