The Raspberry Pi is a fantastic little computer capable of all sorts of things, but unfortunately it only supports one operating system at a time. Berryboot allows you to boot into as many Raspberry Pi operating systems as you want.
Berryboot is pretty self-explanatory. Simply install Berryboot on your SD card and run the program. That will format your SD card and give you an option to download a few of the more popular operatings systems including Rasbian, Sugar and others. You can also add your own operating systems as well, but it takes a bit of work in the command line.
It's easy enough to manually swap operating systems on a Raspberry Pi since they're just installed on an SD card, but if you want to have them all on one card Berryboot is an easy way to do it. Head over to the Berryboot site for the installation guide.