This is the footmisc package originally written by Robin Fairbairns, these days maintained and developed further by Frank Mittelbach.
Package source can be found at:
https://github.com/FrankMittelbach/fmitex-footmisc/
and issues can be logged there
The license is LPPL 1.3c.
Copyright (C) 1995-2011 Robin Fairbairns
Copyright (C) 2018-2023 Frank Mittelbach
https://latex-project.org/