https://www.gamespot.com/articles/free-and-cheap-pc-games-at-gogs-big-summer-sale/1100-6459372/

Anyone who wants to save money on PC games is in luck because GOG has kicked off a massive summer sale, with over 1,000 games available for up to 90 percent off. They're even throwing some free PC games into the mix, some of which are only available for a limited time. The sale runs between now and June 18 and, as always with GOG, the games are DRM-free.

If you go to the page between now and June 6, you can get a free copy of the strategy game Xenonauts with no strings attached. GOG's press release suggests more freebies will be on offer as the sale continues.