client/contactsPackage contacts are for the fundamental building block to HubSpot, contacts.
client/crmassociationsPackage crmassociations covers the CRM Associations API is used to manage associations between objects in the HubSpot CRM.
client/dealsPackage deals covers the Deals API which has been exposed to allow for easy integration with the HubSpot CRM objects.
client/engagementPackage engagement covers the engagements which are used to store data from CRM actions, including notes, tasks, meetings, and calls.
client/ticketsPackage tickets is part of HubSpots preview program, and should be considered as a non-stable release that will be subject to bugs and breaking changes while under development.

Updated 2019-06-28. Refresh now. Tools for package owners.