Discussion and questions on Cassandra's usage and development happens mainly on the following mailing lists:
We have recently moved to the ASF Slack organization for all chat. Please sign up for an account to participate.
#cassandra- for user questions and general discussions
#cassandra-dev- strictly for questions or discussions related to Cassandra development
#cassandra-builds- results of automated test builds
#cassandra-builds-patches- results of patch test builds
You can also check the Q&A about using Cassandra on Stack Overflow.
There are a number of third-party Cassandra projects that could be useful. Check out this listing.
If, after having asked for help, you suspect that you have found a bug in Cassandra, you should report it by opening a ticket through the Apache Cassandra JIRA tracking system. Please provide as much detail as you can on your problem. Don't forget to indicate which version of Cassandra you are running and on which environment.