[Free Steam Key] Earth 2150 - The Moon Project

The game doesn't have a Steam store page but you can still redeem it, they are giving away some other free games as well (Enclave & East India Company Gold Edition) so you can grab them if you missed them before.

1. The site uses Facebook for registration & Steam for redeeming the keys so login both of them first.
2. Go here
3. Signup or login to the site
4. Click "Profile / Keys" in the top right corner
5. Scroll to the bottom & click "Get your Steam key here"

Bonus:

G2A: Hustle And Bustle Weekly Sale - 3% Off Coupon: KINGS

GMG: Hot Deals - 20% off voucher: INDIEK-INGSDI-SCOUNT