Discourse.org
"Discourse" is software created by the hosting company "Discourse.org". To learn more about them: https://www.discourse.org/team . It's not clear if it's a for-profit or non-profit company based on their website.
C4ES discourse.org server
The C4ES currently (as of June 2020) hosts a forum at https://forum.electionscience.org , though they've announced that they plan to freeze activity at the end of July 2020.