You can try LiveAgent Live Chat Software. Apart from live chat it also has ticketing and helpdesk features like: Email, Departments, Priorities, Rules, Canned/Predefined messages, Email templates, ...
(more)Olark and Zopim are pretty much the same considering its functionality. And BTW Zopim is now called Zendesk chat according to acquisition. of Zopim by Zendesk.
Anyway, for growing e-commerce website...
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