Google Fonts

Google Fonts is web fonts that are more beautiful, readable, accessible and open.

Google Fonts makes it quick and easy for everyone to use web fonts, including professional designers and developers by providing quality typography to web pages and applications.

It is a directory of web fonts for the world to use.  They are open source fonts; meaning that you are free to share your favorites with friends and colleagues. 

Also, you can customize them for your own use, or collaborate with the original designer to improve them. 

And you can use them in every way you want, privately or commercially — in print, on your computer, or in your websites.

Many of Google's own web pages are already using Google Fonts, such as Google's About page and Google's World Wonders Project which use Open Sans.