Corda has a developer mailing list, corda-dev. Please subscribe if you are interested in contributing to the Corda platform or just watching the team work.
Corda also has an announcements mailing list, corda-announce. Please subscribe to receive email announcements of new software versions and security alerts.
The welcome email for the corda-dev list is here.
This forum complements the #design channel on Slack. Bug reports and questions about how to write apps should go to Stack Overflow, the #general channel on Slack, or the R3 paid support ticket system.