ALMACAL IV: A catalogue of ALMA calibrator continuum observations
  We present a catalogue of ALMA flux density measurements of 754 calibrators
observed between August 2012 and September 2017, for a total of 16,263
observations in different bands and epochs. The flux densities were measured
reprocessing the ALMA images generated in the framework of the ALMACAL project,
with a new code developed by the Italian node of the European ALMA Regional
Centre. A search in the online databases yielded redshift measurements for 589
sources ($\sim$78 per cent of the total). Almost all sources are flat-spectrum,
based on their low-frequency spectral index, and have properties consistent
with being blazars of different types. To illustrate the properties of the
sample we show the redshift and flux density distributions as well as the
distributions of the number of observations of individual sources and of time
spans in the source frame for sources observed in bands 3 (84$-$116 GHz) and 6
(211$-$275 GHz). As examples of the scientific investigations allowed by the
catalogue we briefly discuss the variability properties of our sources in ALMA
bands 3 and 6 and the frequency spectra between the effective frequencies of
these bands. We find that the median variability index steadily increases with
the source-frame time lag increasing from 100 to 800 days, and that the
frequency spectra of BL Lacs are significantly flatter than those of
flat-spectrum radio quasars. We also show the global spectral energy
distributions of our sources over 17 orders of magnitude in frequency.
