Pidgin - is an instant messenger client that is perfect for people who need to communicate with friends who use different applications, or for those who like a little more control over their chatting. The Pidgin interface is quite simple, which for many is a plus, although it has most, if not all, of the features found on other clients. Obviously, the major plus to using Pidgin is that it can support multiple accounts on different networks, so you'll only need the one interface to chat with all your contacts on all your accounts.
aMSN - is a free open source MSN Messenger clone, with features such as:
Offline Messaging
Voice Clips
Display pictures
Custom emoticons
Multi-language support (around 40 languages currently supported)
Webcam support
Sign in to more than one account at once
Full-speed File transfers
Group support
Normal, and animated emoticons with sounds
Chat logs
Timestamping
Event alarms
Conferencing support
Tabbed chat windows
emesene - is an open source instant messaging client designed for use with Microsoft's .NET Messenger Service. It is a clone of Windows Live Messenger
An examination into MSN Messenger 7.5 contact identification [An article from: Digital Investigation]
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