I'm not one to bag pay-for Windows utilities, but a program called DNDstation from security firm Comodo deserves some attention. It's supposed to prevent apps that might "interfere or interrupt the game play". A 30-day trial is offered and you can buy a one-year subscription for $US5. But why would you when a simple registry tweak can do the same thing?
The tool's primary feature is the ability to stop programs grabbing focus from, or "popping" in front of any "OpenGL or DirectX" game. The thing is, this functionality can be enabled fairly easily with a registry tweak, specifically by altering the "ForegroundLockTimeout" value under "HKEY_CURRENT_USER\Control Panel\Desktop".
Alternatively, just could just close any attention-seeking applications before you play.
To be fair, DNDstation offers to "tune the system resources to improve your gaming experience" and stop scheduled tasks from running while you play, which is nice, but hardly worth $US5 a year.
I'd liked to have tested the program, but the trial version kept crashing on start-up.