  The complexity of modern cosmic ray observatories and the rich data sets they
capture often require a sophisticated software framework to support the
simulation of physical processes, detector response, as well as reconstruction
and analysis of real and simulated data. Here we present the EUSO-OffLine
framework. The code base was originally developed by the Pierre Auger
Collaboration, and portions of it have been adopted by other collaborations to
suit their needs. We have extended this software to fulfill the requirements of
UHECR detectors and VHE neutrino detectors developed for the JEM-EUSO. These
path-finder instruments constitute a program to chart the path to a future
space-based mission like POEMMA. For completeness, we describe the overall
structure of the framework developed by the Pierre Auger collaboration and
continue with a description of the JEM-EUSO simulation and reconstruction
capabilities. The framework is written predominantly in modern C++ and
incorporates third-party libraries chosen based on functionality and our best
judgment regarding support and longevity. Modularity is a central notion in the
framework design, a requirement for large collaborations in which many
individuals contribute to a common code base and often want to compare
different approaches to a given problem. For the same reason, the framework is
designed to be highly configurable, which allows us to contend with a variety
of JEM-EUSO missions and observation scenarios. We also discuss how we
incorporate broad, industry-standard testing coverage which is necessary to
ensure quality and maintainability of a relatively large code base, and the
tools we employ to support a multitude of computing platforms and enable fast,
reliable installation of external packages. Finally, we provide a few examples
of simulation and reconstruction applications using EUSO-OffLine.
