Supports Windows 2000, XP, Vista, 7 and Mac OSX!!!
Licensed under GnuPL, so it’s 100% free and 100% legal for commercial (and non-commercial) uses.
Works very similarly to GoToPC or TeamViewer, with an ID number generated for each client that you get from the user and type in on your end to connect.
It uses a “repeater” as the static component, so as a technician you don’t even need to be in the same place each time; the client connects to the repeater, and so do you. No more static IPs and port forwarding necessary for the technician, just the one repeater machine.
I’ve tested this and my company now has a working version hosted on our website, here:
http://support.st-aubin.com
It works well on XP, Vista, and Windows 7, and although I haven’t actually tested it (since we have so few occasions), I’m sure it works perfectly on Win9x and Win2k as well. No need for the Mac client yet, but it’s ready if/when we need it, as this is our only Mac-compatible remote support at this time.