I have seen these around but I'm not sure if they are bespoke applications.
Basically, I have been tasked by my MD to find an application that will sit in front of my webservers.
When the connections reach a defined limit, a busy message is shown and a cookie written to the client computer.
The page with the busy message automatically refreshes and the client is given an approximate waiting time based on the number of clients trying to connect and the "queue postition" based on the cookie time.
I know this is very specific, but I have seen this in action and I need something similar.
If anyone knows of anything that can do the job I would be very appreciative.