Give your DRM-free collection a boost.
GOG are offering the following three game for free if you spend $15 in their Weekly Sale that ends on September 18, 2017 at 4 PM UTC:
Kyn (list price $19.99).
Tropico Reloaded (list price $5.99).
Breach & Clear: Deadline Rebirth (list price $19.99).
The total list price of those games is $45.97.
Image credit: GOG.com