Pilot combined virtual memory and file storage into one subsystem, and used the manager/kernel architecture for managing the system and its resources.
Its designers considered a non-preemptive multitasking model, but later chose a preemptive (run until blocked) system based on monitors.
[1] Pilot included a debugger, Co-Pilot, that could debug a frozen snapshot of the operating system, written to disk.
A typical Pilot workstation ran 3 operating systems at once on 3 different disk volumes : Co-Co-Pilot (a backup debugger in case the main operating system crashed), Co-Pilot (the main operating system, running under co-pilot and used to compile and bind programs) and an inferior copy of Pilot running in a third disk volume, that could be booted to run test programs (that might crash the main development environment).
This architecture was unique because it allowed the developer to single-step even operating system code with semaphore locks, stored on an inferior disk volume.