This article discusses software internally used by Apple.
Acquiring a copy without Apple's consent is illegal and may result in being scammed.
RestoreTools.pkg is a package seeded to some Apple employees. It contains the following Mac applications: PurpleRestore, PurpleSNIFF, PurpleFAT, DCSD, PurpleBuildSanitizer, a crash dumper, which automatically launches when an iDevice is connected, and an additional panel for Xcode Organizer. The command line version of PurpleRestore is installed as well to /usr/local/bin as well as a handfull of other command line utilities. These applications aren't installed in /Applications like normal. They are instead installed to /AppleInternal/Applications.
When attempting to install restoreTools.pkg on MacOS Mojave(10.14.4) it gives the user an error message and refers them to HomeDiagnostics. It appears that Restore Tools is being deprecated for Home Diagnostics.