shroudBNC is a modular IRC proxy written in C++. It is capable of proxying IRC connections for multiple users. Using TCL scripts it can be extended.
Amongst its features you can find a user-friendly web interface (coded in TCL and PHP) which allows you to easily create and manage users. A live demonstration of the web interface can be viewed here. Some screenshots are also available.
A variety of operating systems are currently supported: Linux, FreeBSD (and possibly other variations of BSD) and Windows.