  We introduce a method to create mock galaxy catalogues in redshift space
including general relativistic effects to linear order in the cosmological
perturbations. We dub our method LIGER, short for `light cones with general
relativity'. LIGER takes a (N-body or hydrodynamic) Newtonian simulation as an
input and outputs the distribution of galaxies in comoving redshift space. This
result is achieved making use of a coordinate transformation and simultaneously
accounting for lensing magnification. The calculation includes both local
corrections and terms that have been integrated along the line of sight. Our
fast implementation allows the production of many realizations that can be used
to forecast the performance of forthcoming wide-angle surveys and to estimate
the covariance matrix of the observables. To facilitate this use, we also
present a variant of LIGER designed for large-volume simulations with low mass
resolution. In this case, the galaxy distribution on large scales is obtained
by biasing the matter-density field. Finally, we present two sample
applications of LIGER. First, we discuss the impact of weak gravitational
lensing onto the angular clustering of galaxies in a Euclid-like survey. In
agreement with previous analytical studies, we find that magnification bias can
be measured with high confidence. Second, we focus on two generally neglected
Doppler-induced effects: magnification and the change of number counts with
redshift. We show that the corresponding redshift-space distortions can be
detected at 5.5$\sigma$ significance with the completed Square Kilometre Array.
