Reverse Proxy Server?

[Dean Thompson <deansub () ev1 net>]

I hope this is the right place to post this...

We develop numerous internal web applications that we occasionally need to 
publish to customers.  In very sensitive scenarios, we will force them to 
use a VPN to connect.  In others, we just publish a server/app beyond the 
firewall.  I would like to see a solution that could handle both scenarios 
easily, and would not require that I put multiple servers or apps outside 
the firewall.

My thoughts were to use something like what Anonymizer 
(http://www.anonymizer.com) does.  Essentially, it just forwards requests 
for you, and returns the information to you.  So, if someone out there went 
to http://mydomain.com and logged in, they could then go to 
http://mydomain.com?server=someserver (or something like that).  Does 
anyone out there know of a tool like this that is already available?  I 
would prefer a Windows platform, but 'nix is acceptable.

Thanks,
Dean