Intel has created and open sourced a font that is very similar to Avenir and I can recommend.
Avenir is the font used in Apple iOS. Even though Avenir has been around for quite some time, it’s modern and fresh looking particular on high resolution devices such as smartphones and printed paper. I also recommended it in a long post on fonts in Network Diagrams: Choosing Better and Free Fonts.
Clear Sans is a versatile OpenType font for screen, print, and Web. We designed Clear Sans with on-screen legibility and glanceability in mind. It strikes a balance between contemporary, professional, and stylish expression and thoroughly functional purpose. It has a sophisticated and elegant personality at all sizes, and its thoughtful design becomes even more evident at the thin weight.
Although this font lacks a condensed version, it is highly preferable to the standard fonts from Microsoft which I generally find lack clarity because they are badly rendered on most devices. I would also prefer Clear Sans over Opens Sans because the rendering quality seems higher to me and there are more weights (more important that you might be aware of).
This font is free and open under an Apache license so that anyone can add it to their Windows, Mac or Linux and is also freely available as a web font for use on your web site.