  Thanks to the success of current gamma-ray telescopes (Fermi, H.E.S.S.,
MAGIC, VERITAS), and in view of the prospects of planned observatories such as
the Cherenkov Telescope Array (CTA) or the High-Altitude Water Cherenkov
Observatory (HAWC), gamma-ray astronomy is becoming an integral part of modern
astrophysical research. Analysis today relies on a large diversity of tools and
software frameworks that were specifically and independently developed for each
instrument. With the aim of unifying the analysis of gamma-ray data, we are
currently developing GammaLib (http://sourceforge.net/projects/gammalib), a C++
library interfaced to Python that provides a framework for an instrument
independent analysis of gamma-ray data. On top of GammaLib we have created
ctools (http://cta.irap.omp.eu/ctools), a set of analysis executables that is
being developed as one of the prototypes for the CTA high-level science
analysis framework, but which is equally suited for the analysis of gamma-ray
data from the existing Fermi-LAT telescope and current Cherenkov telescope
arrays. In particular, ctools and GammaLib provide the novel opportunity of a
simultaneous multi-instrument analysis. We present the status of the software
development, and illustrate its capabilities with a spectral analysis of the
Crab nebula emission over seven decades in energy (1 MeV to 10 TeV) using
multi-instrument (COMPTEL, Fermi-LAT, H.E.S.S.) gamma-ray observations as well
as a simulation of a CTA observation of the supernova remnant RX J1713.7-3946.
