We used Nunito Sans on Riot.im for many years, and had the same experience of tracking down the author only to discover Vernon's tragedy. The font lives on, though - https://github.com/googlefonts/nunito for instance has sprouted a full Cyrillic version since.

http://sansoxygen.com/ is the way to donate to support Vernon's family now (the youcaring.com link seems to be dead).