Since 2013 the ESA Gaia mission is delivering parallaxes with an exquisite precision for over 1 billion stars in our galaxy. But the non-linear transformation between parallax and distance makes it not trivial, specially in the case when the relative parallax error is larger than about 20%. As explained in Bailer-Jones (2015, PASP, 127, 994), estimating distances is an inference problem in which the use of prior assumptions is unavoidable. Estimating the distance to a group of stars (cluster) and properly taking into account the individual uncertainties is also a complex inference problem.
Kalkayotl is a Bayesian inference code designed to obtain samples of the joint posterior distribution of cluster distance, cluster size, and cluster members distances. It was specifically designed to work with Gaia data and corrects for the well known issue of parallax angular correlations.