https://quant.stackexchange.com/

https://stats.stackexchange.com/

https://lifehacks.stackexchange.com/

https://cooking.stackexchange.com/

https://codegolf.stackexchange.com/ - recreational programming competitions

https://softwareengineering.stackexchange.com/

https://codereview.stackexchange.com/

https://worldbuilding.stackexchange.com/ - for writers/artists using science, geography and culture to construct imaginary worlds and settings

https://stackexchange.com/sites - all stackexchange sites

https://cs.stackexchange.com/ - computer science

https://genealogy.stackexchange.com/ - genealogy & family history