How they do it: Amazon offers royalty options for publishers, authors, or other rights holders who want to sell their e-book or other content in the Kindle store. In this model both the rights owner as well as Amazon get parts of the revenue from a sale.
Learn more about Amazon Kindle →
How they do it: Google’s AdSense product enables publishers to serve automatic text, image, video or interactive media ads on its website. These are targeted specifically to the website’s audience (e.g. location and demografic). Content publishers can earn revenue on a per-click or per-impression basis.
Learn more about Google →
How they do it: All 3rd party apps that make revenue with the iPhone users have to give a specific cut to Apple. This applies for AppStore purchases as well as in-app purchases.
Learn more about Apple iPhone/AppStore →
How they do it: Groupon’s core offering is a website connecting customers with businesses offering a service at a discount (coupon). Groupon takes a fee from each transaction / coupon sold over their website after a minimum treshhold of sales is reached. The 3rd party business can profit from more customers and shares part of that revenue with Groupon.
Learn more about Groupon →