http://en.wikipedia.org/wiki/Opera_Software
http://en.wikipedia.org/wiki/Opera_%28web_browser%29
edit: here is a good excerpt
"Up to this point, the Opera browser was trialware and had to be purchased after the trial period ended. But version 5.0 (released in 2000) saw the end of the trial period requirement. Instead, Opera became ad-sponsored, displaying advertisements to users without a license,[8] which was commonly criticized as a barrier to gaining market share. In newer versions, the user was allowed a choice of generic graphical banners or text-based targeted advertisements provided by Google based upon the page being viewed."
Corel probably would have been thrilled to have Adobe make their formats completely open and "standardized" back in the day to reduce the friction of switching products.