Remote desktop software/server

Does anyone know of any remote desktop software, similar to gotomypc, that I could host on my own server? What we are basically looking for is a free/inexpensive solution that requires very little setup on the side of the PC to be controlled, so that we can do remote support from any location. Ideally somethng that doesnt require firewall configuration. UltraVNC has a pretty good single click config, that does what we want on the user end, but from our side we still need to config the firewall. Is there such a beast in the OSS/Linux world? TIA Michael Katz