The R code of hairline is under the MIT License (see the file LICENSE).

inst/fonts/HairlineSans-*.ttf
  'Hairline Sans' is a modified version of Public Sans v2.001
  (https://github.com/uswds/public-sans): tabular figures by default, renamed and subset.
  Copyright 2015 The Public Sans Project Authors.
  Licensed under the SIL Open Font License, Version 1.1, without a Reserved Font Name;
  the full licence is in inst/fonts/OFL.txt.