MaterialX Channel in the ASWF Slack
The official and best place to discuss MaterialX is now on the Academy Software Foundation's #materialx channel, at http://academysoftwarefdn.slack.com/. This venue is appropriate for general questions, feature requests, and discussion of the MaterialX Project as a whole.
To get an invite to join this Slack, please go to https://slack.aswf.io/.
MaterialX Forum on Google Groups
The original MaterialX Discussion Forum on Google Groups is also still available, which may be more suitable for lower-level developer and API questions.