Communication channel
Last year we used the GitLab wall, which does not exist anymore.
Michiel and I tried HipChat, but it requires registration and we were not really impressed.
A mailing list could be an option, but seems a bit overkill and not real-time enough.
Perhaps etherpad.mozilla.org is a good option? We also used that in the software carpentry course at VU Amsterdam.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information