  Aims: The interactive software package iCosmo, designed to perform
cosmological calculations is described. Methods: iCosmo is a software package
to perform interactive cosmological calculations for the low redshift universe.
Computing distance measures, the matter power spectrum, and the growth factor
is supported for any values of the cosmological parameters. It also computes
derived observed quantities for several cosmological probes such as cosmic
shear, baryon acoustic oscillations and type Ia supernovae. The associated
errors for these observables can be derived for customised surveys, or for
pre-set values corresponding to current or planned instruments. The code also
allows for the calculation of cosmological forecasts with Fisher matrices which
can be manipulated to combine different surveys and cosmological probes. The
code is written in the IDL language and thus benefits from the convenient
interactive features and scientific library available in this language. iCosmo
can also be used as an engine to perform cosmological calculations in batch
mode, and forms a convenient adaptive platform for the development of further
cosmological modules. With its extensive documentation, it may also serve as a
useful resource for teaching and for newcomers in the field of cosmology.
Results: The iCosmo package is described with various examples and command
sequences. The code is freely available with documentation at
http://www.icosmo.org, along with an interactive web interface and is part of
the Initiative for Cosmology, a common archive for cosmological resources.
