Thanks Mark for the link, following is my summary from the link
The Centurion® Lounge
Cost: $50/person
Guest allowed: No limit
Escape Lounges
Cost: free
Guest allowed: 2
Delta Sky Club
Cost: free
Guest allowed: no limit (cost unknown)
Same day Delta or Delta connecting flight boarding pass required
Lufthansa
Cost: free
Guest allowed: no limit (cost unknown)
Same day Lufthansa group flight boarding pass required
Plaza Premium Lounges
Cost: free
Guest allowed: 2 (fee?)
Priority Pass Select
Cost: free
Guest allowed: 2
Additional Global Lounge Collection Partner Lounges
Cost: free
Guest allowed: 0?
Please correct me if I have missed anything. Not much free options, I think only Priority Pass Select is the only one you can use widely and that network sucks in US.