ZOHO smiles at you slowly for asking this question. ZOHO is great and gives you an absolute gem of a software called ZOHO Desk. The Desk is web-browser based for a mere cost of 12.00$ per month. It gives you the ease, grace and enjoyment of using a call center software. The Desk also integrates with other software from ZOHO but lacks integration with outside software limiting its usage. Users of the software are pushing ZOHO for a desktop client app but its still in development.
Zendesk is your secondary option for Call Center software. Zendesk charges a dollar per user and is cheaper for large organisations. Zendesk is bland in terms of appearance but covers deeper ground than ZOHODesk with software integration.