From http://www.dd-wrt.com/

DD-WRT is simply a project which is based on the official GPL Sources of Sveasoft Alchemy. Due the nature of GPL based projects, this firmware will be also release under this license. Initially i wrote this modification to make it possible, to use the Linksys WRT54G/GS inside our Wireless Lan network as cheap replacement for our professional Lancom and Orinocco access points. so what was missing? first, we are using radius authentication with a central account management inside our network for user authentication. There is already a radius application available for OpenWRT, but openwrt was no choice since it is not user friendly for a non computer professional without any linux knowledge. so i just integrated it with some small enhancements in the alchemy software. my wrt-radauth modifications:

radius server timeouts will not be a problem anymore. a client is authenticated just up to the point, the server says really 'no'. a connection timeout will not have any influence to this workflow.

additionally i found it really helpfull to use a external filesystem device inside the WRT. my choice was a samba client since it is useable on any computer platform. you can easilly mount a windows network share into the wrt and additionally its also possible to start a script after mounting from this device. but the work was not over. also if currently the server/client watch function is still under development, i already implemented the RFlow traffic monitoring and management tool into the web interface. this tool is already inside DD-WRT, but you have to start it manually and so far it looks unfinished. (daemon mode does not work). so i finished it and yes now its working inside my DD-WRT and you can configure it out from the administration window.