Some free/paid to use platforms to make an online community:
AnswerCart: https://www.answercart.com/
Discourse: https://www.discourse.org/
Threadbase: https://threadbase.io/
Tribe: https://tribe.so
Mighty Networks: https://www.mightynetworks.com/
Telescope: http://www.telescopeapp.org/
Mobilize: Mobilize | Membership Community Platform