WordPress 2.5

Code name: Brecker – Released date: 2008
This version of WordPress was released in the year 2008 and had the most beautiful UI of WordPress till then according to me. It was from this version when the WordPress UI started to look like what it is right now. With the introduction of this version the file uploader was revamped with a new look and a few essential features to go.
For the first time in WordPress history, users were now able to upload multiple images or other post attachments at once and finally get to know how much time the uploads will take with the help of a progress bar.

WordPress 2.7

Code name: Coltrane – Released date: 2008
By this time, WordPress had grown rapidly and reached thousands of bloggers, prepped with great ideas for great sites, all roaring to go. The entire framework of the Admin Panel UI has changed, and a sidebar consisting of links to essential tools needed to manage a WordPress powered site was added to the panel giving quick access to needed tools.
The Admin Panel was divided into different sections such as “Publish”, “Tags”, “Comments” and more which gave rise to the addition of two useful features in this update, “Screen Options” and “QuickPress”.
While “QuickPress” made posting easier and faster right from the Dashboard, “Screen Options” helps in cleaning up your writing space as well as dashboard, and have it the way you want not what is fixed by the developers. Some other features include 1-click plugin install, rearranging sections on dashboard and more.

WordPress 3.2

Code name: Gershwin – Released date: 2011
We move ahead to the year 2011 to a refreshed and modern UI for WordPress with the introduction of version 3.2. The UI has changed a lot, completely redesigned, while at the same time, keeping the CSS light so as to load the panel a whole lot faster.
This version features another a great tool “Full Screen Editor”, which provides a distraction-free writing experience. Also the Admin Bar was given some love too, and with the addition of new features such as 1-click addition of new post, new user, etc, it became a handy tool to manage your WordPress site easily.

WordPress 3.5

Code name: Elvin – Released date: 2012
WordPress 3.5, which is the current available version of WordPress, was made available to public in December, 2012. Though the overall UI seemed unchanged or changed to a very little extent, but I am interested in the “Media Manager”.
The media manager seems wonderful and offers a spectacular way to manage all your media for your blog. This version is made ready for the Apple Retina screen, supporting High-Resolution version of the Admin panel, so no matter which device you are using to access your blog’s backend it will surely look great on every device.

What’s Next?

So, we finally reach the current version of WordPress and the journey ends here… until the release of WordPress 3.6. This is a screenshot of a plugin developed by Matt and his team to change the current WordPress Admin Panel UI to a brand new look.

WordPress 3.6

It is expected that they will adapt this new look as the UI for WordPress 3.6. Though not much details are available for this new release, but everything will be confirmed when the official version is released.
Source:hongkiat.com