App Request: Only custom ringtones ring

[icedice34]

On an old phone, I had a setting where it was basically alarm only. However, it would allow custom ringtones to ring. This is handy to set the phone on silent so no one can call, but my fiance, or parents could call in an emergency since they have custom ringtones. I'm sure there is an application out there that allows me to do this. Anyone know what it is?

Thanks!