In no particular order, here are some good links for basketball referees and fans (after my “Double Whistle” Facebook page!)
FIBA Rules and Interpretations (FIBA Document Library)
NBA Rules (2018-19)
National Basketball Referees Association (NBRA) 
National Basketball Association (NBA)
EuroLeague
7Day EuroCup
Eurohoops (multi-language)
Sportando (multi-language)
Referee.com
Basketball in Europe (Facebook page)
Crown Refs (on Twitter)