Open Sans in action on iteratehq.com

.header-1 { font-family: "Open Sans", "Helvetica Neue", Helvetica, Arial, sans-serif; font-size: 54px; font-style: normal; font-weight: 300; letter-spacing: normal; line-height: 54px; text-transform: none; color: #1A1A25; }
.header-2 { font-family: "Open Sans", "Helvetica Neue", Helvetica, Arial, sans-serif; font-size: 23px; font-style: normal; font-weight: 100; letter-spacing: normal; line-height: 32.66px; text-transform: none; color: #A4AAB3; }
.content-1 { font-family: "Open Sans", "Helvetica Neue", Helvetica, Arial, sans-serif; font-size: 17px; font-style: normal; font-weight: normal; letter-spacing: normal; line-height: 50px; text-transform: none; color: #FFFFFF; background-color: #4E3083; }
Open Sans is available from Font Squirrel, Google Web Fonts, MyFonts and Typekit.

Try this combination out in Pair and Compare.
Found by @mikesten on 11 Aug 2016.

Liked by:
@mikesten @Vyacheslav300 @pixelcutlabs

Open Sans