Mac
* MSN Messenger
* Psi
* QQ
* Skype
* Windows Messenger
* Yahoo! Messenger
Other
* Akeni
* BitWise IM
* FotoSwap
* Gadu-Gadu
* Gossip Corporate Messenger
* Instan-t
* LanTalk NET Corporate Messenger
* LanTalk XP LAN Messenger
* Lotus Sametime
* My Messenger
* Omnipod
* Sonork
* talk
* TiVi
* Tlen
* Xfire
Multi-protocol
* Adium
* Agile Messenger
* aMSN
* Ayttm
* BitlBee
* BlowSearch Secure Messenger
* Centericq
* Colloquy
* Easy message
* Everybuddy
* Fire
* Gaim
* Hello
* InstantCharts
* iChat
* IM2
* IMVITE Video/Audio/Multi-chat
* Konnekt
* Kopete
* Milkbone
* Meetro
* Miranda IM
* naim
* ngIM Client
* Odigo Messenger
* Proteus
* Regnessem
* Qnext
* SIM
* Trillian
* Yamigo (for mobile phones)
Single protocol
* Kadu
* Licq
* mICQ
* Sticker
* Trele Morele
Jabber protocol
* Coccinella
* Exodus
* Google Talk
* Gabber
* Gajim
* JAJC
* Psi
* Tkabber