A free app for Android, by Episode Apps.
The best way to stay safe on the internet is to have an idea of who is contacting you. With the Caller ID app, you can see the phone number of anyone who is calling you. This way, you can know if it is someone you need to talk to or if it is someone you need to avoid.
The app works like a contact book. You can also add people to your blacklist. If the number is on your blacklist, the app will not allow you to call them. You can also identify people who are on your blacklist by looking at the phone numbers. You can add people to your whitelist to allow calls from them.