Blue Robotics Forum
The Blue Robotics forum is a community of marine roboticists and ArduSub users. This is a great place to ask questions, and share your projects and ideas.
The ArduPilot Forum is a community of ArduPilot users. There is a lot of information on troubleshooting, hardware and software developments, and technical projects.
The Blue Robotics gitter is a chatroom to discuss Blue Robotics and Ardusub matters, we're happy to help anyone who drops by.
The ArduPilot gitter is a chatroom for ArduPilot developers, for technical discussions about pull requests and code changes.
The PX4 Slack (QGC) channel has an ongoing discussion about QGC development.