Apple has a new support page up urging customers to migrate their libraries out of Aperture, for the end is nigh for the photo editing application:
In June 2014, Apple announced the discontinuation of development of Aperture. Since that time, Apple has released five major macOS updates. For technical reasons, Aperture will not run in future versions of macOS after macOS Mojave. To continue working with your Aperture photo libraries, you must migrate them to the Photos app included with macOS, or migrate them to Adobe Lightroom Classic.
Aperture’s history is mixed at best, but I know its user base was quite loyal in the day. This news shouldn’t come as a surprise, but I’m sure there will be users scrambling to escape this sinking ship.