I've just learned that Version 2.1-beta of the World Historical Gazetteer is live at https://whgazetteer.org

"It introduces Place Collections, authored sets of individual WHG place records meaningfully connected on any theme, and which can be annotated. Place Collections can be made public and optionally include e.g. related links, images, and a PDF file. Some may recognize the new Place Collections as an implementation of the #LinkedTraces concept."

https://whgazetteer.org/tutorials/placecollections/