GOG also has a Halloween Sale 2019.

It will last until 04.11.2019.

SteamWorld Quest: Hand of Gilgamech, the new card based RPG from the developers of SteamWorld Dig and SteamWorld Heist, is now also available DRM-free for Linux on GOG!

For the RPG Pathfinder: Kingmaker the so called "Enhanced Edition" has been released:

The EE includes:

For Stellaris the new (paid) DLC "Ancient Relics" has been released for Linux on GOG and Steam.

Also Stellaris is currently available for free on GOG Connect, and the huge Update 2.3 ("Wolfe") has been published!

A huge patch 1.6.0 and a new (paid) DLC "Urban Warfare" are now available for Linux on GOG and Steam!

Urban Warfare brings 'Mech combat to the vast cityscapes of the Inner Sphere! Electronic warfare, large-scale building destruction, environmental mechanics, new enemy units and more make the urban sprawl a whole new battlefield.

A new (paid) DLC for the management game Railway Empire is now available for Linux on GOG and Steam: France.

New scenario – Into a new time (1874-1890)

Map expansion: France (available in Free Game and Sandbox modes)

10 historical engines such as the Coupe Vent (4-4-0) and Forquenot (2-4-2)

For the city building simulation "Surviving Mars" the huge Armstrong Update has been released for Linux.
At the same time the DLCs "Green Planet" and "Projekt Laika" have been published.
Both DLCs are part of the season pass.