Fur.ly allows you to shorten multiple websites into a single shortened URL. Enter as many URLs as you want, klik go, then you will be provided with one single shortened URL. So when people visit the link, it has a fur.ly toolbar at the top that allows them to switch which URL they want to visit.
This would be very useful if you want to send someone some or lots of websites. Instead of provide with so many links, you just only send one link that will come up with all the websites that you want to pass to them.