Truecaller is an app that identifies unknown calls and blocks spam calls and unwanted SMS.
Features: When a number that is not saved in your contacts calls you, Truecaller automatically shows you the name and business associated with the number, using a huge social database. There is also caller ID and call recording (depending on the country).
Pros: It significantly reduces nuisance and scam calls, which is very important for people in countries where phone fraud is more common. There is also SMS filtering to filter out malicious messages.
Cons: The app requires special permissions to access your contacts, which some people have privacy concerns about.
Conclusion: If you are bothered by unknown calls, Truecaller is a useful tool that allows you to find out who is calling you before you answer.