Hi I am thinking of creating a new Blogging platform on my website where my site visitors can register and create their own blog address. i.e., if my website is xyz.com, they will be able to create a blog at xyz.com/user where they can login and post their own blog. Is there any open source software that I can install to achieve this? Your help is very much appreciated.
Wordpress.org has a multisite function from version 3+. It can do what you describe. It's basically the same thing that powers wordpress.com and many other big blogging sites. Beware, however, that sites like this are heavily targeted by spammers and that you will need to take precautions to avoid/minimize this. It's a big undertaking. Good luck!
Here it is: http://codex.wordpress.org/Create_A_Network#Step_3:_Allow_Multisite It was called wordpress multisite in the pre 3.x times. B.