Free Web hosting Control panels and their Features
ISPconfig: Good solution, it is more of a GUI controlling tons of vps functions (Apache/nginx, mysql/mariaDB/Postgre, php, mail, ftp, firewall etc) than a simple control panel. It can create resellers and users with moderate control of their account.
Little tricky to install it (you have to manually install all elements as Apache, mysql, php, mail, ftp etx.) but has best tutorials on how to setup in several flavors. Just see howtoforge or search google, there are extremely detailed instructions on over than 50 different configurations).
Good and easy interface for end users, can interact with whmcs.
Webmin/Virtualmin: A web control panel that has it all, but it has weird interface for noobies and end users. Tons of options (not just a control panel) but it need good knowledge of handling a server and administrate linux. You can do almost anything to maintain/control/update/fix your server (vps, dedi etc) and your sites, but it is difficult to tune it. You have to be an experienced user, if no, do not use it in production environment.
VestaCP: Easy to install, easy to use, it lacks on functions. For basic vps managing, it is fine. Very easy for the end user.
Ehcp: No frequent updates, but still active especially for patches/fixes (latest patch is on 11/9/2014). Good and nice interface and option to use different ones (there are 8-9 different layouts in-the-box). Easy, stable and lightweight, but works only in Debian/Ubuntu likes.
Zpanel (now Sentora): PROS: Very good and stable control panel, very easy to handle especially for end users. CONS: Had many many many security problems in the past, that the community behind it says there are not existing any more.
BE CAREFUL: providers and programmers here still saying that this software has a lot of security holes and the Zpanel/sentora community does not willing to fix them or even to admit that there are holes (I am not a programmer, do not have this kind of knowledge of coding, so, I cannot have mine opinion on that. But with so many warnings from LET Community, you should be careful).
UPDATE: Sentora Community has new owners than the zpanel past. Bobby Allen has quit the new community due to conflicts with the owners of zpanel project (he sold zpanel to hostwings some months before but I think now his relation with them is not good, so, he decided to withdraw from both projects for now). The team now is leaded by some old dev members and some new, and has grown up a bit. I don't know if this is a change to a good direction for making sentora more secure, time will show. But their community is up again and most of people there seem to be willing to help and listen to criticism. Again, time will show...
Kloxo: No, nein, niet, ohi, no way. It was the king of the free cpanels once, now it is an almost dead project, weird and dysfunctional in today's standards, with a ton of security problems and outdated. Stay away
Kloxo-MR: Mustapha's fork of Kloxo. He is the main developer and did a good job to close Kloxo's holes, update it with many functions and fixes, he is active and he is doing a good work. But there are still issues (functionality, ease of use etc.) as it is a fork that has been built on original Kloxo.
There are some more:
i-MSCP (medium, lack of options, clean and easy interface)
Froxlor (medium, lack of options, clean and easy interface)
Ajenti (based on Ajenti server control panel, not easy interface, not tested by me, I only installed it once to play a little with the interface, didn't like it)
Bailfox (very minimal interface, has all basic options though. Not tested by me)
ISPconfig (need work from you to install it, but very easy for your end users)
VestaCP (very easy to install, very easy for end users, minimum options to control though)
Virtualmin/webmin (Very easy to install it but very tricky to configure/tune it. Difficult interface for administrator and for end users, recommended highly but only for experienced users)