Digsby is a Social & Communication software developed by dotSyntax, LLC. After our trial and test, the software is proved to be official, secure and free. Here is the official description for Digsby:

Digsby is a instant messaging, email notification and social networking tool. Digsby=IM+Email+Social Networks.

Key Features:

Instant Messaging
One combined Buddy list for all your AIM, MSN, Yahoo, ICQ, Google Talk, Jabber, and Facebook Chat Accounts.

Manage multiple conversations with tabbed conversation windows. You can drag tabs out into their own windows for important conversations.

Rename contacts with an alias so you don't have to remember buddy names like 'giantsfan123'.

If one of your friends has more than one IM account you can Combine them into a single merged contact to eliminate duplicate buddies.

Send your friends SMS messages right from the IM window.

The InfoBox lets you check everyone's status message and profile just by moving your mouse down the list.

Email
Manage your Hotmail, Gmail, Yahoo Mail, AOL/AIM Mail, IMAP, and POP accounts right from digsby.

Get popup notifications when new email arrives. Clicking a popup takes you right to the message with auto-login into webmail accounts.

The email InfoBox gives you a snapshot of your unread messages with just one click

Social Networking
Stay up to date with everything happening on your Facebook, Twitter, MySpace and LinkedIn accounts.
Receive alerts of events such as new friend requests, messages, group invites, etc.

Personalize
Customize digsby with application skins to give it a personal look and feel.

Change the way your conversations look with themes – everything from simple AIM-style windows to 3D conversation bubbles.

Complete control over the layout of buddies on the buddy list. Change everything from buddy icon size to whether or not to show a snippet of their away message.

Other

Digsby offers complete synchronization between computers and installations. Everything from the skin you chose to your pre-defined status messages follows you from place to place.

You can place a widget on your blog, website, or social network profile so you can chat with visitors right from digsby.