exodus VS gramps

Work code (although, not a sample database) here --> https://github.com/MinchinWeb/exodus

Why does it have to be a web app? It does not meet your requirements, but when I looked into this sort of task before, the best option looked like Gramps [0], which was discussed at [1].

  [0] https://gramps-project.org

Depends and what are you interested in and if you prefer a particular programming language eg if you are good in say PHP I'd suggest helping the MantisBT project a bugtracker used by a lot projects. https://github.com/mantisbt. or say Python and enjoy genealogy I'd suggest going for Gramps https://github.com/gramps-project/gramps .

Maybe share more info on what you like so we suggest something you might enjoy?

Is there a reason to prefer Webtrees over an open source desktop app like Gramps?

https://gramps-project.org/

Source code. ( zip / tar.gz )

May be you can look at an example. 1) Try to see how is defined geo map creation on Geography View in Gramps, a genealogical program in full Python giving these kinds of maps

My technique is to maintain my tree off line in Gramps and do online work in the always free FamilySearch.

Alternatively, there's Gramps (free): https://gramps-project.org/

Unfortunately, the default layout in the relationship graph is for spouses to not be side by side, but hopefully this will be fixed in a future version of gramps.