i need a chat an online chat plugin for wordpress website like in this site see the live chat area which also mentions departments as well like sales technical support etc.
I use phplive for my brand based clients with an actual budget. The stuff those folks are using is crazy expensive. This is an awesome alternative... https://www.zopim.com/ EDIT: actually I am not sure what they are using but I will flesh it out but I suspect I know that is. And, its expensive lol..
Nigel's suggestions are very good. I used WHMCS with the live support but that is actually a separate addon by Stardevelop. I'm not so crazy about them for reasons I won't discuss here. It works although it is more eye candy than anything else. Back in the day livezilla was a great free alternative with a premium package. Kayako is solid all around and an excellent suggestion.
Comm100 Live Chat maybe a good option for you. It's easy to set up & use. http://www.comm100.com/livechat/