Reddit

Reddit is a very large online community.

Rationalist and rationalist-adjacent forums you might include:

• /r/LessWrong - LW type discussion
• /r/LessWrongLounge - more casual LW discussion
• /r/VoluntaristLWBookClub - defunct book club

• r/slatestarcodex - SlateStarCodex

• /r/rational - Rationalist fiction
• /r/hpmor - HPMOR
• /r/OfficialHPMOR - HPMOR (mysteriously closed oooOOOooo)

• /r/rokosbasilisk - Roko's basilisk
• /r/rokosrooster - I can't even

Ones you might not like include:

• /r/SneerClub - SneerClub