Wikipedia
SHAREit is a free application to transfer files from a Wi-Fi compatible device to another similar one. Users can use it to transfer files including photos, videos, music, contacts, apps and any other files. It is a free application from Lenovo that allows Windows, Windows Phone, Android, and iOS devices to transfer files directly by ad-hoc Wi-Fi connections. It is currently available in 39 languages including English, French, Spanish, Russian, Arabic and Chinese. It was first launched In China in June 2012 and known as anyshare. In transfer field, SHAREit competes with Xender, Zapya, Share Apps, SuperBeam. In addition to transferring files, SHAREit’s services also include CONTROL and CLONEit. Shareit's Windows Phone app is now named SHAREit [Official] and the older app renamed to SHAREit [Unofficial] which was developed by Paradox.
The app offers faster speed than Bluetooth and even NFC, and it's totally secure, considering the type of connection it uses to transfer files. Prior to SHAREit or similar applications, the only best method for file transfer was either through Bluetooth, or USB drives. In case of Bluetooth, the speed was adequate, while the USB drive case had a negative side. That negative side was the chances of getting malicious data or file transferred from one device to another, thus, hurting the foreign device or PC in connection. This was noted by various renowned universities and even magazines like WIRED. Looking at the unsafe protocol offered by USB drives, and slow speed of Bluetooth, applications like SHAREit were developed, based on Wi-Fi Direct methods.