  In this work we present spectra of all $\gamma$-ray burst (GRB) afterglows
that have been promptly observed with the X-shooter spectrograph until
31-03-2017. In total, we obtained spectroscopic observations of 103 individual
GRBs observed within 48 hours of the GRB trigger. Redshifts have been measured
for 97 per cent of these, covering a redshift range from 0.059 to 7.84. Based
on a set of observational selection criteria that minimize biases with regards
to intrinsic properties of the GRBs, the follow-up effort has been focused on
producing a homogeneous sample of 93 afterglow spectra for GRBs discovered by
the Swift satellite. We here provide a public release of all the reduced
spectra, including continuum estimates and telluric absorption corrections. For
completeness, we also provide reductions for the 18 late-time observations of
the underlying host galaxies. We provide an assessment of the degree of
completeness with respect to the parent GRB population, in terms of the X-ray
properties of the bursts in the sample and find that the sample presented here
is representative of the full Swift sample. We constrain the fraction of dark
bursts to be < 28 per cent and we confirm previous results that higher optical
darkness is correlated with increased X-ray absorption. For the 42 bursts for
which it is possible, we provide a measurement of the neutral hydrogen column
density, increasing the total number of published HI column density
measurements by $\sim$ 33 per cent. This dataset provides a unique resource to
study the ISM across cosmic time, from the local progenitor surroundings to the
intervening universe.
