I am doing a Stanford Open Course(CS 107 Programming Paradigms). Is there a free UNIX OS that i can practice the assignments on? In assignments they require a Leland Unix environment which requires a Stanford account. I need an alternate OS.
There are any number of UNIX-like OS around. Some of the more popular branches include Linux (especially Debian, Fedora, etc), BSD, and the more recent versions of Mac. What are you trying to do with it? If all you need is some stuff with a Bourne shell, you could probably even do that with Cygwin on Windows...
Well as NT says, Linux is "Unix like". If you have no experience of using anything other than windows, you might find it easier to install a Linux distribution like Ubuntu or Debian instead of true Unix FreeBSD.
FreeBSD can take a lot of time to configure it to how you want. For example, you will not automatically get a GUI desktop set up with FreeBSD. You will have to configure that yourself. But most Linux distributions have basic configuration such as a desktop, done for you.
You don't have to use emacs to compile your programs. Emacs is just a text editor that also allows you to compile code (and do a few other things). You could simply use an ide like codeblocks if you want to keep using windows for the course.