Quasars probing quasars X: The quasar pair spectral database
  The rare close projection of two quasars on the sky provides the opportunity
to study the host galaxy environment of a foreground quasar in absorption
against the continuum emission of a background quasar. For over a decade the
"Quasars probing quasars" series has utilized this technique to further the
understanding of galaxy formation and evolution in the presence of a quasar at
z>2, resolving scales as small as a galactic disc and from bound gas in the
circumgalactic medium to the diffuse environs of intergalactic space. Presented
here, is the public release of the quasar pair spectral database utilized in
these studies. In addition to projected pairs at z>2, the database also
includes quasar pair members at z<2, gravitational lens candidates and quasars
closely separated in redshift that are useful for small-scale clustering
studies. In total the database catalogs 5627 distinct objects, with 4083 lying
within 5' of at least one other source. A spectral library contains 3582
optical and near-infrared spectra for 3028 of the cataloged sources. As well as
reporting on 54 newly discovered quasar pairs, we outline the key contributions
made by this series over the last ten years, summarize the imaging and
spectroscopic data used for target selection, discuss the target selection
methodologies, describe the database content and explore some avenues for
future work. Full documentation for the spectral database, including download
instructions, are supplied at the following URL
http://specdb.readthedocs.io/en/latest/
