This is omnical, a module for redundant-baseline calibration of interferometric visibilities (Liu et al. 2010). It was used for Zheng et al. (2014) and Ali et al. (2015) and early HERA analysis.
Omnical has been superceded by hera_cal's redcal module, but is being kept here for legacy purposes. There are no plans to update or maintain this repo.
A memo explaining omnical's mathematical operation here, along with a comparison to redcal.