What are some alternatives?
When comparing Illustrio and Font Awesome, you can also consider the following products
Evie by unDraw - MIT licensed illustrations for your next project
Flaticon - A database of free vector icons.
DrawKit - MIT licensed SVG illustrations, in 2 styles
Google Fonts - Making the web more beautiful, fast, and open through great typography
IcoMoon - IcoMoon is an icon management tool that is build to provide iconography.
IconPharm - IconPharm is a library of open source icons with recoloring and resizing tools.