The French INED provides an interesting and customizable simulator which allows the user to anticipate the demographic evolution in specific geographic areas:
https://www.ined.fr/fr/tout-savoir-population/jeux/population-demain/
Entering specific criteria in the system allows the user to evaluate the impact of e.g. the fertility rate, etc. An interesting tool for statisticians and planners!
Blog de Filogis traduction 