I use a mixture of linux and windows machines at my office. I've got logmein running on my windows machines, and VNC setup on the linux ones. The linux logmein browser plugin works great. However, I'm confused as to why there are no services like logmein or gotomypc for linux where you just install the program and you're good to go because there's no port forwarding to setup in your router. Is this because those services use port 80 to handle their communications which would be open? Is there a need to setup servers to handle the redirection so it wouldn't be cost-effective to create an open source RDP client/server suite that didn't require port forwarding?
Apps like TeamViewer are [Client--Server--Client]: they depend on using a server external to both parties' local networks. Each end is a client and initiates its own connection to the external server. Firewalls and NAT routers generally pass outgoing connections quite freely, and NAT enables the replies (coming from the external server) to reach the right internal nodes (PCs).
True [Client--Server] services require the server to have a routable address. A PC providing a service from behind a NAT router doesn't have a routable address, only the router nearest the internet has one. So an incoming connections for a given IP and port# has to be routed to the specific local-network node (PC) known your router to serve that particular port -- i.e., Port Forwarded.
Indeed, most of the "plug and play" apps (if you will) have a negotiation server in between you and the other machine which help connect you together via an ephemeral port. TeamViewer is a good example. It has native builds for Windows and Mac, and will run under Wine on Linux.
I would be surprised if such software for Linux didn't already exist. Have looked for that functionality for Linux outside of Logmein and gotomypc? If very little does exist my guess would be for security concerns.
Is there a reason why you couldn't use SSH? I would recommend using it for security reasons and getting that port to be opened by security people isn't hard to do once security mechanisms are in place.