One of the open-sources of free fonts in Creative Commons (CC-BY-SA 3.0) licenses. But you can allowed to use my free fonts and don't ask the note, comment and e-mail spamming, because they are annoying.
See also in Creative Commons of CC-BY-SA 3.0 - [link]
And also choose a license - [link]
CC-BY-SA was approved in Free Culture works, but it's free to use.