www.beyondallreason.info

Looking at it, the engine is GPL: beyond-all-reason.github.io/…/choose-recoil

But while BAR releases their source, it isn’t really open source (no derivatives): for example, with the many of the art assets, “all rights reserved”: github.com/…/license_general.txt

It does look good, that said.

The Recoil engine is interesting to me. It’s not something I’d seen before in the open source ecosystem (sometimes I live under a rock). I suspect the underlying mechanisms (although written for RTS games in the Total Annihilation family) might permit implementing something like a Paradox game with some tweaking.