The best place to ask questions for specific issues related to MPS. Frequented by MPS devs, and other users with a lot of experience. Beginners have their own Slack channel, more advanced users can leave questions in the main Slack channel.
The Slack channel has organised a weekly Office Hours meetup where the author of the Specific Languages blog post talks through problems that users bring to them. Very helpful, whether you’re learning how to tackle a problem in MPS, or if you have more specific questions.