It's not like you can't google yourself some install instructions. Also, this "article" doesn't bring anything new. You can get this information from the REE documentation.
Please, stop voting on this :(
You just copied chunks of upstream documentation, and added the copypasta <pre> blocks of sudo apt-get install... that are the hallmark of Ubuntu blogspam.
Yeah, it doesn't "invent" anything new, but it's doesn't have to and it's far from being spam. Many people found my article useful and even the authors of Passenger thought this was well done.
The objective of blogging is sharing knowledge. I had these notes on a wiki of mine as I recently setup a couple of servers, so I thought I'd share them.
Basic overview of its architecture: http://github.com/blog/517-unicorn