Is there any opensource application that can substitute the WHM/cPanel functions? As long as the application could do the per user/domain level permissions and management, that would do.

Webmin/usermin would be your best choice out of the freebies

Webmin is much less obnoxious than cPanel.

If you want to debase your system with somthing with a bazzilion dependancies that will use half your RAM and let you pretend there is no such thing as a command line, there is ISPconfig.

http://www.ispconfig.org/

There is a support forum for it at howtoforge (which is an awesome site btw).

http://www.howtoforge.com/forums/forumdisplay.php?f=14

Yea, I have noticed about ispconfig. I wonder how many commercial public sites are using that one. And any comments on the followings? web://cp Zantastico Zpanel

Another good Control Panel that is pretty cheap is ServerCP I think its like $7-$10 a month and Very very nice. I have a couple of my dedicated customers that use it and rave about it.
I also use Webmin too and like it.
-Pete

Webmin/usermin would be your best choice out of the freebies

ya it is really a good choice, i think support will be a problem ( tech support )

I have used webmin a few years ago but have never used usermin. Does that support user quota, file manager, mysql mgmt, ftp accounts mgmt, email accounts mgmt, etc.. ?

Just checked that and found out it has limited and can't compare against cpanel. Is there easy way to include phpbb installer into the usermin? And can the modules like ssh could be removed?

Depending on your linux distrobution, the webmin modules should be configurable on an individual basis. I strongly recomend using packages provided by the distro when at all possiable and not the upstream source files. They are easier to install, easier to configure, easier to update and easier to remove if you don't like them.

I think virtualmin is the name of the modual you want.

Many distros have phpbb packages. That's as close as you're going to get for an installer.

Phpbb3 has a sweet web installer btw. It took me less than ten minutes to install.