Shown below are some screenshots of Retrogen (running on a Macbook Air with Ubuntu 20.04 and programmed using GnuCOBOL) using a publically available family tree for President Kennedy (via Ian Davis GitHub). This GEDCOM file was uploaded to Ancestry and subsequently, this tree was exported from Ancestry with some minor data cleansing.
The first screenshot shows the main module for loading or saving a GEDCOM file.
After loading and reviewing any warnings, the view module shows the family view of parents and children of the selected individual and their spouse.
To navigate through the family tree, the mouse can be used to select individual ids or it is possible to display a list of individuals within the family tree.
Alternately, a pedigree family view can be used to show direct ancestry lines.
Unfortunately, the family tree I choose to share these screenshots of Retrogen did not have citations, sources with their repositories or media.