While not always RISK-specific, the Epic Games Store offers a rotating selection of high-quality free PC games every week that often includes strategy titles.

Be cautious of websites offering "Free Downloads" of delisted games. These are often unofficial "abandonware" sites or pirated copies that can carry significant security risks, such as malware or viruses. Alternative Ways to Play RISK

This is the current official version available for free (with in-app purchases) on Steam, iOS, and Android. It features cross-platform multiplayer and various maps.