Roboto

Roboto is a sans-serif typeface designed by Christian Robertson, ParaType, Font Bureau, added to Google Fonts in 2013. It's available in 9 weights, as a variable font.

This is one of 9 character sets supported (cyrillic, cyrillic-ext, greek, greek-ext, latin, latin-ext, math, symbols, vietnamese). Being free and open source, it's a great choice for web projects, print, and branding — and it's a frequent result in the font finder.

Putting it on a site? See the guide to using custom fonts on the web.