[overu589]

ACL: the trickiest part was the surprisingly few lines of dense code that performed inclusions and exclusions of various lists (allow, deny, omit). Sure it was complicated also in the way it interfaces everywhere as seamlessly and unobtrusively while still being eminently useful.

Configuration management stack: this I got multiple cracks at throughout my time, ultimately what it sounds like. From fs through db and cache; cascading layers from defaults, installation, instance, profile, and running settings. And acts like an ordinary associative array everywhere used.

Though there are other examples of self rolling solutions for heterogeneous systems deployment (before ansible and piper).

What was most complex in all of this was keeping things in the end very simple.