Source Sans Pro

Source Sans Pro is a sans-serif font. It goes well with Montserrat, Open Sans, Work Sans, Industry, Quebec Serial, Novecento, Vollkorn, Bitter, Bebas and Sofia Pro Soft. If you're thinking about using Source Sans Pro then try 38px for headers. Give 20px a shot for content.

People commonly tag it as modern, clean, portfolio, design, simple, security, agency, sans serif, blog and app. You can get it from Font Squirrel, Google Web Fonts and Typekit.