Howdy! Welcome to our community of more than 130.000 members devoted to web hosting. This is a great place to get special offers from web hosts and post your own requests or ads. To start posting sign up here. Cheers!
I checked out zpanel, and it has a positive feel to it. I registered with the Forum and looks as though its being run by an expert group from the UK: http://www.zpanelcp.com/about/team/
Its last release is 1 January 2013. I'm not an expert even by a long shot, but I'd have thought there should have been an almost immediate new release after its hacking experience at the beginning of this month. Just get the feeling that it has security issues and isn't updating its software often enough. I may try it out one of these days however just to see how it works.
You could have a look at Kloxo, DirectAdmin and Zpanel. I can also recommend you Webmin. It's a website control panel and of course a free one. I have been using it for some time and it has been great alternative to cPanel.
I've used webmin for a lot of "cloud" boxes. But that's on each individual vps and not for an entire environment. It has just about everything cpanel has, more direct access and a nice little ajax console for shell.
I think they sell a product called cloudmin, or you could just install webmin on each box.