Ask HN: What are the best slack groups/communities you are part of?

I'd love to hear what Slack groups you all are part of, and why? What value are you getting? What do you love? What annoys you?

I am specifically interested for members of my team Slack groups aimed at: - COOs - CTOs - CMOs - Heads of Product - Product Mangers - Project Managers - Dev Ops - Software Developers in RoR, Angular, etc etc...