I will likely get dirty looks for querying the CCDB directly but I'm a recovering DBA. API endpoints are nice, I like database queries. If you don't know how to connect to the CCDB database you probably shouldn't be using this blog post :)

To get the list of Organizations and the number of application instances they've started in the last 7 days:

SELECT  
  sum(processes.instances) as app_instance_count,
  organizations.name
FROM  
  processes, 
  apps, 
  spaces, 
  organizations 
WHERE  
  processes.app_guid=apps.guid and 
  apps.space_guid=spaces.guid and
  spaces.organization_id=organizations.id and
  processes.state='STARTED' and 
  processes.created_at > DATE(NOW()) - INTERVAL 7 DAY 
GROUP BY  
  organizations.id, 
  organizations.name 
ORDER BY 1 desc;  

To get the list of Organizations and how much RAM their running application instances have reserved:

SELECT  
  sum(processes.memory * processes.instances) AS memory_reserved,  
  organizations.name 
FROM  
  processes, 
  apps, 
  spaces, 
  organizations 
WHERE  
  processes.app_guid=apps.guid and 
  apps.space_guid=spaces.guid and
  spaces.organization_id=organizations.id and
  processes.state='STARTED' 
GROUP BY  
  organizations.id, 
  organizations.name 
ORDER BY 1 desc;