Indiegala offers Steam key downloads of Humanity Asset for Windows for free when you join Indiegala's Steam community group and register your email. (Scroll down to find the game.) That's tied with our mention from last fall and the lowest price we could find by $10.
You'll need to link your Steam and Indiegala accounts to activate the game. (If you don't already have one, you'll need to create an Indiegala account.)