The same origin policy
I wanted to make a community wiki regarding HTML/JS same-origin policies to hopefully help anyone searching for this topic. This is one of the most searched-for topics on SO and there is no consolidated wiki for it so here I go :)
The same origin policy prevents a document or script loaded from one origin from getting or setting properties of a document from another origin. This policy dates all the way back to Netscape Navigator 2.0.
What are some of your favorite ways to go around same-origin policies?
Please keep examples verbose and preferably also link your sources.