The Swedish Koha User Group uses the Mattermost platform for communication, in-between physical meetings arranged by the member libraries. The address is https://matters.lub.lu.se/koha.
The platform is open for members only and has restricted access, contact any member of the steering committee for more information if you wish to join. Apart from personal invitations it is possible to add domains, so that anyone with an e-mail address for that domain can create an account and log-in.
The Swedish Koha User Gorup also has a wiki, with more information and documentation, at the address: http://koha.se/wiki.
The GitHub used by the User Group is found here: https://github.com/koha-se.