ConfigMgr : Query to find all non-client and unassigned machines (computers and servers)

Just create a collection and use the following query :

select SMS_R_SYSTEM.ResourceID,SMS_R_SYSTEM.ResourceType,SMS_R_SYSTEM.Name,

SMS_R_SYSTEM.SMSUniqueIdentifier,SMS_R_SYSTEM.ResourceDomainORWorkgroup,

SMS_R_SYSTEM.Client from SMS_R_System where Client = 0 or Client is NULL and

SMSAssignedSites is NULL