Roboto, the popular default Android font, is open source and free to use.
Roboto, the default font for Android, is an open source and free alternative to Helvetica.
Roboto’s lowercase letterforms are slightly thinner than Helvetica’s. Roboto Font is optimised for screens. It may look a little familiar to users when used in an Android app, but we recommend it for other uses. Because its letterforms are slightly thinner and therefore more compact, it works best for busy, important user interfaces where space is at a premium and cannot be wasted.