Avoid exec() calls whenever possible
At many places in the code, exec() calls are issued.
This is bad for many reasons, one being the portability of such code is very restricted, and another is about security (audits).
Leveraging UNIX command-line tools usage would also lessen/cancel the importance of setting a sensible PATH (see http://www.howtoforge.com/forums/showthread.php?t=47801).
Those should be replaced by PHP native code whenever possible.
This is a tedious task, error-prone and with little immediate perceived advantage, though it has to be done to improve ISPconfig code quality.
I'm not directly volunteering, but I will try to do my best to improve the current situation, without breaking anything.
I would bet that running ISPconfig on Windows is not so far away, given this work is done (but I'm certainly not interested).