Tool for working remotely with two PCs connected both via NAT-routers

Hi everybody,

the configuration:
PC A connect via a NAT-router to the Internet
PC B connect via a NAT-router to the Internet

PC_A[local_IP]---[local_IP]-NAT-router(A)-[public_IP]---((INTERNET))-

-((INTERNET))---[public_IP]-NAT-router(B)-[local_IP]---[local_IP]PC_B

I know about the problem of port forwarding to make this conception work.

But, my question is: Is there any (hopefully freeware) tool, which can
connect
two PCs for working remotely through firewalls/routers/proxies without
setting
up forwarding rules? The reason for that is that sometimes you don't have
any access to configure firewall rules.

For example, if you have a look at Skype messaging, the problem should be
the same as it is with remote-control-software if you're working with
firewalls/
routers/proxies. But this works, because Skype is using a central server
which
connects you.

Is there a tool which can achieve this using a Skype-like concept or maybe a
better one?

Thank for your help.

Oliver.