Symbly makes use of a variety of paid and open-source software to function, including:
SymbolStix Symbol Set by News 2 You
SymbolStix is a fantastic symbol set originally created for use in the News 2 You online service. You can purchase a separate subscription to the set through SymbolStix online if you’d like to use the symbols in other tools or software besides your Symbly supports. SymbolStix © 2003-2012 News 2 You, Inc.
Straight Street Mulberry Symbol Set
The Straight Street Mulberry symbol set is a creative commons licensed set of symbols freely available for use in any project. You can find out more information at their site.
Noun Project Symbols
The Noun Project endeavors to create a set of public domain and creative commons licensed symbols to aid everyone in understanding the world around them. Symbly includes symbols from this set that are licensed to the public domain. You can read more about the Noun Project on their site.