Split your browser window in two! Add any site you like as a sidebar to other sites.
Have you ever wanted to see your keep notes while browsing your email on gmail? This open source extension allows you to do just that!
Merge sites you frequently use together and visit them at the same time!
Some of the popular sites like Facebook or Twitter use an iframe inside their sites to track users, so you won't be able to use them as split without opening Chrome with a special flag.
Check https://github.com/NicoSantangelo/Split-It for more info, sorry!