Freemium

https://en.wikipedia.org/wiki/Freemium

Org
http://www.freemium.org/

Forbes
http://www.forbes.com/search/?q=freemium

HBR
https://hbr.org/search?term=Freemium

Guide
https://www.zuora.com/guides/is-freemium-right-business-model/

Insider
http://www.businessinsider.in/searchresult.cms?query=freemium

Slides
http://www.slideshare.net/search/slideshow?searchfrom=header&q=freemium

Tube
https://www.youtube.com/results?search_query=freemium