A simple way to block access to the internet per app
...NetGuard’s interface is simple, with toggles to allow or deny access and optional settings for screen-on behavior, roaming, system apps, and notification of internet usage, giving users fine-grained control over network behavior.
Server/client suite which provides per-user access control/firewall/QOS. Robust and high speed implementation is secure against MAC/IP spoofing, and can scale to large networks with many clients. Options for additional monitoring and captive portal.
Nubric (Near-real-time user behaviour and resource interaction control) is a framework for security and authentication-related modules written in Java. Its origin focus lies on network monitoring, dynamic, transparent firewalling and traffic control.