Truecaller - Find a person by a name or phone number worldwide for free using Truecaller.
FullContact Card Reader - Automagically scan biz cards into LinkedIn/Gmail contacts
CallApp - Free Caller ID & Call Blocker app that allows mobile users to block phone calls, identify calls, blacklist unwanted callers and much more.
Google Contacts - Google Contacts is Google's contact management tool that is available in its free email service Gmail, as a standalone service, and as a part of Google's business-oriented suite of web apps Google Apps.
CallerSmart - CallerSmart is an application that is basically used for the purpose of looking up mystery phone numbers for free.
Nextcloud Contacts - The Nextcloud contacts app is a user interface for Nextcloud's CardDAV server.