Gramps.js is the responsive Javascript frontend of Gramps Web, a modern web app that allows to browse and collaboratively edit a genealogical database, based on and interoperable with the Gramps desktop application. See Gramps Web API for the Python backend repository.
A demo deployment based on the Gramps example family tree is available here.
The documentation for using or developing Gramps.js can be found on the Gramps Web documentation site.