SyncToy is a nice backup tool from Microsoft that is sadly not supported or even offered for download anymore.
The best download opportunity IMO is from archive.org (https://web.archive.org/web/20190427065841/http://download.microsoft.com/download/6/c/4/6c406239-a648-4e01-833e-2c452deed3b6/SyncToySetupPackage_v21_x64.exe) since this should be a snapshot from the original Microsoft site.

To be able to install SyncToy, the installer asks for a specific .NET version. This version is included in the .NET Framework that can be installed in Windows by

  • hitting the Windows Key and typing „Turn Windows features on or off.
  • selecting „.NET Framework 3.5 (includes .NET2.0 and 3.0)

Install SyncToy afterwards.