Though not free (it comes bundled with Microsoft Office), Century Gothic is remarkably similar to Futura and is legally licensed for your use.

Designed by Paul Renner and released in 1927, Futura was born from the Bauhaus movement. Renner rejected the ornate, serif-heavy styles of the past, opting instead for a typeface based entirely on geometric shapes—the circle, the square, and the triangle.

: It was the font used on the commemorative plaque left by the Apollo 11 mission.