Metrics and Alerts can both be used outside of the Hawkular framework so really you can store any metric you like, or alert on basically any data you like.  As for Events, the next release of Hawkular Alerts (0.6.0) will include a new Events feature that you may find interesting.  Whereas Alerts are relatively rare, typically involve human interaction, and run through a simple life-cycle; Events are likely much more numerous, representing any sort of happening that a client wants to persist.  The interesting thing about Events in HK-Alerts is that they can be inserted directly via API or can be generated via Trigger, like an Alert.  And Events can also be used as Trigger conditions, to contribute to further Alert or Event generation.