These days Adobe is releasing more open-source applications (e.g. the new WebKit-based code editor, Brackets). The Adobe type team felt they–and the community at large–needed a better option for on-screen work.
Thus they’ve created Source Sans Pro. As the Verge notes, “[T]his family of fonts is intended primarily to be used in user interfaces, meaning it has to be legible at low resolution yet also readable enough to support long streams of text.” Designer Paul D. Hunt explained some of his process & considerations for the project, adding:
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.