As an Atlassian app vendor, we facilitate the entire Atlassian suite of tools to support our users and our own processes:
A Jira based issue tracker
A Jira issue collector in each app allows to Provide Feedback right where you encounter issues with while using our apps (if you are logged in here, the issue will be submitted as you, otherwise anonymously)
A Jira service project should be available in the near future - see https://utoolity.atlassian.net/browse/UAA-22
A Confluence based wiki
A Confluence Questions based questions & answers site, obviously
A Confluence based knowledge base
Of course, you can always get in touch with us directly as well.
We also use Hipchat and are contemplating to open up a room for anyone to join, but are not quite ready yet for this - see https://utoolity.atlassian.net/browse/UAA-39