Includes some things not obviously war-related, e.g. I found some Select Cemetery Registers accessible. Despite being provided by Ancestry UK, it says you get access to records from around the world.
See
https://www.ancestry.co.uk/c/remembrance-day?You need an Ancestry UK registration (free), even if you have one for another country, and may have to enter via the above link.
It's unclear whether it finishes at the start or end of Monday, so don't leave it too late.
As always with free periods, save anything of interest on your own device, as you'll need a sub to see it after the offer closes.