A 3rd party software application.
How do you want to host it? Can you install an agent on each client machine? If so – a complete IT software/hardware support application like <a href=”http://www.ilient.com/free-help-desk-software.htm”>SysAid Free Help Desk Software</a> would automatically fetch license information for you from each machine. I found SysAid easy to navigate, but the client agent model doesn’t fit our network structure.
<a href=”http://www.keyfiler.com/”>Keyfiler</a> is a free web app to file all your license info, but I haven’t personally used it.
I hope these two applications give a good start to finding the right solution.