Avenir in action on nylas.com

.header-1 { font-family: AvenirLTStd-Light; font-size: 40.6px; font-style: normal; font-weight: 500; letter-spacing: normal; line-height: 56.84px; text-transform: none; color: #5B5B5B; }
.content-1 { font-family: AvenirLTStd-Light, sans-serif; font-size: 18.2px; font-style: normal; font-weight: normal; letter-spacing: normal; line-height: 24px; text-transform: none; color: #5B5B5B; }
Avenir is available from Fonts.com, Fontshop and MyFonts.
Found by @mikesten on 26 Apr 2017.

Liked by:
@mikesten @Joshua_D_

Avenir