Here is a free service that lets you can look at any site back in time. You can see how it looked weeks, month or years back. Click on http://archive.org/web/ . Its a site that is an internet archive of websites. As of Aug 2014 it had an archive of 426 billion pages. Aptly titled as INTERNET ARCHIVE – USING WAYBACK MACHINE. There is also an option Save Page Now to Capture a web page as it appears now for use as a trusted citation in the future.
There is also a subscription service that enables you to capture, manage and search collections of digital content without any technical expertise or hosting facilities.
For programmers you can use waybackmachine API to build your own tools.
How to use wayback machine
Punch in the site url you want to see. Click on the button “BROWSE HISTORY” and you will be shown a timeline & calendar with round aqua button around the date. Click on it and you will be able to see how your site looked on that date. You can scroll back & forth to look at site snapshots for other dates.
Example showing a site using wayback machine
Click on link below –
Now click on the aqua buttons on the dates. You will see a snapshot of the site. Click on the timeline at the top to go back in years.
Snapshot of codrops.com when seen using Wayback Machine