Instant messaging/chat Pidgin

Pidgin is Instant message all your friends from one place.
Pidgin is an easy to use and free chat client used by millions. Connect to AIM, MSN, Yahoo, and more chat networks all at once.
Supported chat networks:

* AIM
* Bonjour
* Gadu-Gadu
* Google Talk
* Groupwise
* ICQ
* IRC
* MSN
* MXit
* MySpaceIM
* QQ
* SILC
* SIMPLE
* Sametime
* XMPP
* Yahoo!
* Zephyr
and more you can used plugin bellow
There are third-party plugins for some protocols:

Protocol Name	Website	Short Description
Facebook IM	Go	Facebook social network
Gammu	Go	Protocol to send SMS through your phone via usb/serial/bluetooth/irda
Mail.ru Agent (mrim-prpl)	Go	Russian network
Mail.ru Agent (pidgin-mra)	Go	Russian network
Microblog	Go	Twitter/Identica/Laconica updates
msn-pecan	Go	Alternative MSN access
MXit	Go	MXit IM
NateOn	Go	Korean network More info
NetNexus	Go	netnexus.com's chatrooms
Netsoul	Go	French network
Ning	Go	Ning-based social networks
OkCupid	Go	OkCupid.com dating website
Omegle	Go	omegle.com's web-based random chat
Rediffbol	Go	Indian network
Skype IM	Go
SIPE	Go	Microsoft Office Communicator, Reuters Messaging
Tlen.pl	Go	Polish network
Twitter Protocol	Go	Twitter Buddylist Protocol
WinMX Peer Network	Go	File sharing network
Xfire	Go	Gaming network

Security and Privacy :

Plugin Name	Website	Short Description
bOt_tOOls	Go	Configurable plugin for auto-ignoring yahoo spammers
Bot Sentry	Go	Stop spam bots
Off-the-Record Messaging	Go	Encrypts conversations and provides security even when keys are compromised
Pidgin-Encryption	Go	Encrypts conversations using stored RSA keys
Pidgin-GPG	Go	Pidgin GPG/OPENPGP (XEP-0027) Plugin
Pidgin-Paranoia	Go	Encrypts conversations using one-time pads
Pidgin-privacy-please	Go	Stop spam bots

Interface tweaks :

Plugin Name	Website	Short Description
Adium to Pidgin themes converter	Go	Allows to convert themes from Adiumxtras site
Autohide	Go	Buddy list improvements like autohide, always on top and hide min/max buttons
autoresize	Go	Automatically update the buddy list to fit its contents (vertically).
Character Counter	Go	Plugin for displaying the character count of the current message.
Extended Buddy List Sort	Go	Adds more buddy list sorting options
Hide Chat	Go	Hides the window/tab for a channel when it is joined (useful for auto-join channels)
keys per minute	Go	Counts the keys per minute while you are typing a message and displays it.
Manual Resize	Go and Go	Allows manually resizing the conversation window entry area.
pidgin-cmds	Go	Various conversation commands
Pidgin Conversation Locker	Go	Prevent closing of important conversations(/tabs) by selectively locking them.
Pidgin Conversation Save Order	Go	Save the order of chats and IMs and restore it the next time you open a conversation.
pidgin-nudge	Go	Shakes your conversation window when you receive a nudge/buzz/zap
Pidgin Personal Bar	Go	Adds a section at the top of your buddy list to change your display name and personal message.
Pidgin Windows Position Manager	Go	Places new conversation windows intelligently in Windows (i.e. doesn't always put them in the top left corner).
Protocol Icon Override	Go	Lets you pick the protocol icon to display per-account
Quote selected text	Go	Quick specify message to answer
Scroll to bottom	Go	Scrolls chat history of created conversation windows automatically to the bottom.
Session Save	Go	Session Save will remember what conversation windows you had open the last time you used Pidgin, and re-open them for you when you sign on.
Smiley Shortcuts	Go	Inserts a smiley on ctrl+(number) combination.
TooBars	Go	Add toolbar, status bar, context menu to Pidgin buddy list, hide main menu, change all status by menu (not through Statusbox!) and much more
TooButtons	Go	Add Send and Close buttons to Pidgin conversations
Toolbar Shrink	Go	Shrinks the toolbar of the conversation windows by hiding the text of the buttons.
WrapMenu	Go	Wrap main menu if it is too wide
Windows 7 Taskbar	Go	Adds new Windows 7 eye-candy such as task bar menu, progress and emblems
Xfer Auto Path	Go	Allows you to automatically set the folder for saving your incoming file transfers by some criteria such as buddy alias.

And more...
you can download from here.