UltraVNC

I can use port 80 or 443 of course. That's not the problem.

The way pchelpware works is server -> repeater <- viewer

The issue is that the server is behind a firewall and does not allow it to open tcp connections directly. It can, however, use an http proxy. I do not believe pchelpware can ...

But the server will not use HTTP proxy,right?
It will simply try to connect via TCP to port 80 or 443. In some setups, only http requests that pass through the proxy are allowed (and IE is configured to use it).

Is it possible for the server to use HTTP (with and without http proxy) to connect to the repeater/viewer? Alot of customers are behind firewalls that do not allow opening TCP connections, but obviously allow http connections.