SharePoint Licensing - ugh!

Demystifying SharePoint server licensing
https://vigneshsharepointthoughts.com/2016/06/02/demystifying-sharepoint-server-licensing/

Offical Microsoft Sites
http://sharepoint.microsoft.com/en-us/buy/Pages/default.aspx
http://sharepoint.microsoft.com/en-us/buy/Pages/Licensing-Details.aspx

Mixed Environment
http://thecloudengineer.blogspot.com/2012/02/cal.html

Third Party Sites
Web App
http://www.infoworld.com/d/developer-world/twists-and-turns-office-web-apps-software-license-895