Overlord is arriving on Linux plataform next 21st of July on Steam. Will GOG receive the update tomorrow, too?
https://www.gamingonlinux.com/articles/overlord-for-linux-release-date-announced-arriving-tomorrow-the-21st-of-july.7680

It’s available for OS X too. Would be amazing to get it!

Currently not available on Steam either.

A later update says the Linux and Mac versions are exclusive to another store:
http://mailout.syncode.co.uk/mailout_projects/VP_News/Overlord_FB/index.html?r=uuthbd

Let's wait for this is not definitive.

This database extract suggests that something might happen.

It would be pretty foolish to stick with this weird shop.

I sent an email to Codemasters to see if they will shed some light on this. Hopefully they will. I never understand why the Linux version of so many games don't get put on stores other than Steam.

Codemasters responded to the Linux question. Their response is

"Thank you for submitting your recent request to Codemasters Customer Services concerning Overlord.

Please contact Virtual Programming regarding the Mac or Linux version of the game:

https://www.vpltd.com/

Codemasters are only the developers and publishers of the PC game, not the Mac or Linux version, I'm afraid.".

I tried to contact Virtual Programming via their website but received an error on multiple browsers when doing that so I messaged them on Facebook.

I tried to contact them right after the release of Overlord: Raising Hell but had the same issue.

Both Overlord and Overlord 2 are both available on the Mac with Steamplay now.

Linux too. :-)