SHAREit is a simple Lenovo tool for sharing files over wifi.
There are none of the usual network complexities. If you want to send a file, all you have to do is click Send, drag and drop the files to transfer, and click Next.
If you've installed SHAREit on another nearby device, and it's running, then this will appear on the list of recipients. Click that device and it'll be transferred just as fast as your wireless connection will allow.
This can be particularly useful if you'd like to back up a mobile device to your PC. Click Send and you're able to select all your photos, videos, contacts, files etc with a tap or two, before transferring them to the receiver.
The SHAREit site also talks about the ability to stream photos from an Android device to a PC, or use an Android device to control a PowerPoint presentation. We couldn't get either of these to work and the very basic documentation didn't help, but fortunately SHAREit's file sharing abilities are more than enough to justify the download.