Microsoft Communicator. If you're in a big company that already uses MS Exchange for emails then it's a pretty easy integration. Probably not a great solution for small companies due to the cost.
We predominantly use our feet. Unless someone's snowed in, sick, or subcontracted (and not local) we just walk on over to their desk and talk. Or, hold an ad-hoc meeting. When someone's physically absent from the office, we have no standard policy (though Skype is common).
<a href="http://talkerapp.com/" rel="nofollow">http://talkerapp.com/</a> - to me it's essentially Campfire but free<p>Skype is good too but be careful if you use it for IM. I frequently receive messages hours after the other person sent them, even if we're both online. This is starting to make me not want to rely on it other than for voice/video.
Lync.<p>Pros:<p>-Outlook Integration<p>-Screen Sharing<p>-Decent UI<p>Cons:<p>-Literally the worst copy & paste implementation I've ever seen.<p>-No third party chat protocol integration. (I want to integrate Facebook and Google's Jabber).<p>Edit: Formatting.
We use Google+ for loads of internal communication. It's easy to restrict posts to our organization via Google Apps.<p>While I've not seen any use to adopt G+ in a public way, it's been a phenomenal internal comms tool for async sharing, discussion and debate that isn't critical enough to go on an everyone@ email list.
<a href="https://hall.com/" rel="nofollow">https://hall.com/</a><p>Pros: integration with PT and Github rules; mobile client is better than decent.<p>Cons: transcripts/history can be wonky; no way to add metadata to file uploads; native OS X client seems to randomly eat characters when typing.
Why is 'email' not an option? Which is by FAR the most commonly used internal communication system - although I do NOT recommend it!<p><a href="http://teamstinct.com/but-whats-wrong-with-email" rel="nofollow">http://teamstinct.com/but-whats-wrong-with-email</a>
Humbug: <a href="https://humbughq.com/signup/" rel="nofollow">https://humbughq.com/signup/</a><p>Still pretty new, and in closed beta. But it adds an interesting threading/topic model onto the typically chaotic stream of most group chat apps.
Internal XMPP. Poor ejabberd isn't handling our growth in traffic very well and gets oomkilled and/or swaps itself to death with depressing regularity, so we're trying prosody (over the protests of the internal-IRC faction).
VoIP, email and very occasionally an internal messenger. The idea is not interrupting others too lightly, since we already have scheduled meetings. If something needs dealing with urgently, then these measures kick in.
Dont believe there is no QQ :D
<a href="http://im.qq.com/online/index.shtml" rel="nofollow">http://im.qq.com/online/index.shtml</a>