A free app for Android, by Caller Games.
This is the best caller ID and spam blocker app you will ever need. With a trusted spam list curated from submissions of more than 200 million users, you can freely identify and block spam calls. It helps you find who is the true caller, even if the number is not in your contacts.
You can use XCaller wherever you are! Moreover, XCaller is free and does not come with any in-app purchases.
If you see a number in your phone that you think might be spam, you can add it to the list in the app and it will get blocked.