What a gorgeous font it is! It comes in four varieties: Regular, Medium, Semibold and Bold.
It turns out that Proxima Nova Sans was designed for use as a webfont in the header text throughout the MyFonts website.
Up until last weekend we had been using Arial Rounded MT Bold for our logo, basically because lack of something better, but with this font it looks so much better! So we purchased both the web and desktop version of the Proxima Nova Sans font and have started to use it immediately as you can see in this news article.