Stronghold HD and A.D. 2044 are free for 48 hours at GOG.com
pic.twitter.com/AUwalXaxv6
Thanks to @Madway for the below link:
https://www.gog.com/game/polish_giveaway_pack
Edit: Posting links to the individual games below, but you cannot get them free on their respective store pages, only from the banner at the top of the main page or link above to giveaway pack.