About two weeks after Apple released iTunes 12.7, it made a "legacy" version of iTunes available for enterprise customers that retained app management and installation -- but it is an unsupported configuration.
The iTunes 12.6.3 download was first spotted on Reddit, and is neither secret, nor was it a release intended for the consumer audience. The installer is designed to be the main install of iTunes, and will supersede any prior iTunes 12.7 installation.
It also adds support for iOS11-specific devices, like the iPhone 8, and iPhone X that was lacking on versions of iTunes prior to 12.7.
Despite the ability to perform a bi-directional synchronization eradicated, the ability to install apps and ringtones wasn't completely purged with the jump to iTunes 12.7. Users can still drag and drop properly signed .IPA files (apps), and .m4r (ringtone) files to a device connected to iTunes 12.7, and they will still install.
Apple notes that iTunes 12.6.3 is unsupported, and that the company only provides assistance for the latest version of iTunes. The company suggests that enterprise customers rely on Volume Purchase Program, and the Apple Configurator for enterprise environments.
The download is available for Mac and PC. Given the discovery of the page on by the Reddit user base on Sunday, it is unclear if Apple will leave the download link active, or how long it will actively support the configuration.
As mentioned by Apple in a popup window displayed after installation, iTunes 12.7 places emphasis on music, movies, TV shows, podcasts, and audiobooks. Absent from that list is the App Store, which was previously incorporated as a means to preview, purchase and manage iOS apps on registered devices.