Adobe has released a free/open typeface called Source Sans Pro. It's licensed under the SIL Open Font License, which is considered a free license by the Free Software Foundation. The font itself is beautiful, and comes with a set of supporting files that show how the font was developed and are intended to serve as a guide for follow-on designs.
We realize that the majority of users interested in this project will likely only want the fonts. For this purpose, there is a Source Sans font package that includes just these resources. The family currently includes six weights, from ExtraLight to Black, in upright and italic styles. The fonts offer wide language support for Latin script, including Western and Eastern European languages, Vietnamese, pinyin Romanization of Chinese, and Navajo (an often overlooked orthography that holds some personal significance for me). These fonts are the first available from Adobe to support both the Indian rupee and Turkish lira currency symbols. Besides being ready for download to install on personal computers, the Source Sans fonts are also available for use on the web via font hosting services including Typekit, WebInk, and Google Web Fonts. Finally, the Source Sans family will shortly be available for use directly in Google documents and Google presentations. Full glyph complement specimens (793K) are available in the Adobe type store along with informational pages for each style.
In making these fonts open source, it is important to us to make all the source files we used in their production available so that they can be referenced by others as a resource on how to build OpenType fonts with an AFDKO workflow. The full package of source files can be obtained from the Source Sans download page on SourceForge. As part of this ongoing project, we are publishing a roadmap of features that we plan to implement in the near future. At present, this includes items such as expanding the fonts to provide Cyrillic and Greek support, as well as producing a monowidth version of the Source Sans design.