Spartan MB from Matthew Bailey is a free open source font family based on League Spartan, including 7 weights; thin, light, regular, semibold, bold, extra bold, and black. This typeface includes fractions, ligatures, alternates and is multilingual.
A note from Matthew:
League Spartan is a free open source font that I've used for my personal brand for quite some time. I've loved it like a best friend. Without that single storied a, angled verticals on the M, or rounded tails on the t, I would surely be lost. So, I killed it.
Because as great as this font was, it only had one weight: bold. As you can imagine, body copy didn't look too great in it. Even worse, any alternatives I could find were either more expensive, less than identical, or both. So, since it was an open source font, I set to work adding more weights to it.