The fonts were originally developed by Steve Matteson as Ascender Sans and Ascender Serif, and were also the basis for the Liberation fonts licensed by Red Hat under another open source license. In July 2012, version 2.0 of the Liberation fonts, based on the Croscore fonts, was released under the SIL Open Font License.
The fonts are also available at Noto fonts repository at Github.
A comparison between Calibri and Carlito in some of the more different glyphs.
In 2013, Google released an additional Crosextra (Chrome OS Extra) package, featuring Carlito (which matches Microsoft's Calibri) and Caladea (matching Cambria).  These two fonts are respectively metric-adjusted versions of Lato and Cambo, both available on Google Fonts.