  More than 20 years after the end of NASA's Compton Gamma-Ray Observatory
mission, the data collected by its Imaging Compton Telescope (COMPTEL) still
provide the most comprehensive and deepest view of our Universe in MeV gamma
rays. While most of the COMPTEL data are archived at NASA's High Energy
Astrophysics Science Archive Research Center (HEASARC), the absence of any
publicly available software for their analysis means the data cannot benefit
from the scientific advances made in the field of gamma-ray astronomy at higher
energies. To make this unique treasure again accessible for science, we
developed open source software that enables a comprehensive and modern analysis
of the archived COMPTEL telescope data. Our software is based on a dedicated
plug-in to the GammaLib library, a community-developed toolbox for the analysis
of astronomical gamma-ray data. We implemented high-level scripts for building
science analysis workflows in ctools, a community-developed gamma-ray astronomy
science analysis software framework. We describe the implementation of our
software and provide the underlying algorithms. Using data from the HEASARC
archive, we demonstrate that our software reproduces derived data products that
were obtained in the past using the proprietary COMPTEL software. We
furthermore demonstrate that our software reproduces COMPTEL science results
published in the literature. This brings the COMPTEL telescope data back into
life, allowing them to benefit from recent advances in gamma-ray astronomy, and
gives the community a means to unveil its still hidden treasures.
