Ubuntu Font Family
The Ubuntu Font Family are a set of matching new libre/open fonts in development during 2010--2011. And with further expansion work and bug fixing during 2015. The development is being funded by Canonical Ltd on behalf the wider Free Software community and the Ubuntu project. The technical font design work and implementation is being undertaken by Dalton Maag.
Both the final font Truetype/OpenType files and the design files used to produce the font family are distributed under an open licence and you are expressly encouraged to experiment, modify, share and improve.