CNC hobbyists are hard-pressed to justify spending $3000-$10000 on software for programming when such a price can easily exceed what they have spent on machinery or tooling. Economy of time is usually not as important, so it is hard to justify spending that much money on CAM. These users will probably benefit the most from this project.
A professional will probably not want to use Apt for their day-to-day work, since graphical systems are faster. However, a small shop may only rarely need some of the higher end 4 and 5 axis functions of their machinery, and cannot justify the considerably higher expense for continuous 4 and 5 axis CAM graphical programs. For these times, Apt might offer a solution.
Apt can have variables referenced like other languages. This makes it a parametric cam system that is a time-saver for parts that are similar to one another. In some cases, a complete program for a new part can be generated by changing a few numbers and re-running.
Many programs have been written over the years in Apt, and it is possible that references to these files still exist and can be used. I understand that in the aircraft industry, many planes from earlier eras are still flying and need replacement parts. The B-52 first entered service in 1955, and the last was built in 1962. It is not scheduled to be retired until 2050.
Apt has some features that are rarely found in other Cam systems. For example, if a machinist needs to program a path defined by a math function, many cam programs make this awkward. Some examples include the involute gear tooth profile, the epitrochoid of the Wankel engine, and the cycloidal profile of the roots-type blower.
There are very few open-source cam packages. Most cam packages are Windows based, and expensive.
Apt has a long history, going back to approximately 1958. The Apt360 package includes the IBM source in Fortran H, and demonstrates how things have changed since the 1960's.