Adobe releases Source Sans Pro

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.

More information over on Adobe Typography blog - Source Sans Pro
Adobe Font Development Kit for OpenType