https://www.gog.com/promo/20200914_dwarrows_sale

Besides, GOG silently added some games to the Weekly Sale.
I will mention games that I did not see when I clicked the promo page last time.
Maybe you will find more.

https://www.gog.com/promo/20200914_weekly_sale
Lumo, different editions
Lake Ridden and its DLC

I may be wrong, but there seems to be no announcement for Frogware Sale:
https://www.gog.com/promo/20200921_frogwares_sale

https://www.gog.com/promo/20201003_legend_of_keepers_sale

https://www.gog.com/promo/20201003_darq_sale

Gonner seems to be 89% off currently (without apparent connection to running sales)

https://www.gog.com/promo/20201012_the_quest_sale

https://www.gog.com/promo/20201012_kingdom_under_fire

Elderborn is on sale 40% off


https://www.gog.com/game/elderborn

https://www.gog.com/game/elderborn_metal_af_edition

This sale gives an additional bundle discount when you buy both Kingdom Under Fire games, which as far as I can see is not mentioned anywhere else.

https://www.gog.com/promo/20201015_profesional_farmers_sale

Professional Farmer: Cattle and Crops is out of the development stage.