Ive used skadate before even tho they advertise it as a script for a dating site its got some pretty nice social networking themes 2
My recommendation would go to PHPFox...I've used PHPFox in the past and I've used SocialEngine and PHPFox is the much better route to go!
It is difficult to say which one is the best, it depends on personal skills. PHPFox, SocialEngine, JomSocial those are good one
There are only just a few good social networking scripts around. Actually 3 well known and solid, they exist for many years already and have good support too and private forums. phpFox - http://www.phpfox.com (the best of the 3 if you get the COMMUNITY version with all features) Social Engine - http://www.socialengine.net Jomsocial - http://www.jomsocial.com (this is a Joomla component, Joomla itself is free)
I also can recommend www.Skadate, it is a professional paid script, generally it is for dating community, but it is good for any other community site too. You can choose from free templates, also they offer support, that is very good. Try Oxwall - social networking script, it is free. There are free and paid templates for this script on the site. You can add functionality by installing extensions from plugin category. To start community free without special technical knowledge use Wall. Choose your domain and start your networking site in minutes. After you can use your own domain name or move your community to oxwall script.
MSN inviter is a standalone IM that can be inbuild. For example 123flashchat.com has one. Please check. It'll be a custom work to inbuild this feature into SocialBiz.pro software.