telGuarder is a website as well as mobile phone application that can tell you whether the unknown number that called you is a nuisance call or not.
If you've been receiving nuisance calls and want to know who the caller is and what they're trying to say, then the most likely thing to do is just Google their number. There are websites such as White-pages that will reveal to you not only who he is but also his history.
telGuarder is such a website that speaks in addition to Greek and many languages and provides corresponding information for each country you declare to it. In its Greek version it is a particularly useful tool as it displays all the recent evaluations of phone numbers, along with user comments.
In addition to having a free app for Android and iOS, it can simply work from a browser. Simply go to their website, enter in the relevant field the number you want and see what other users write about this number.
You will also see various statistics, such as how many searches this number has had, how many references, what date the last search was, and a graphical table of fraud or safety rates.
Also an equally worthwhile app is truecaller and you can find it for free on the Play Store.
How I would like a machine. Unfulfilled dream.