All the VNC variants offer an interesting way of getting around firewalls.  Suppose you want to login from home to your computer at work, but there’s a firewall installed at work.  They’ve locked out the incoming ports.  You can use the VNC Viewer in Listening mode to defeat that by triggering an outgoing connection from work to home using, say an email filter to run the command “winvnc.exe” -connect <your home IP number>” and having the VNC viewer listen on your home computer (vncviewer.exe -listen  or similar).  All you do is send the triggering email to yourself at work which activates the vnc server to connect to your home computer.

Perhaps the easiest way yet to remotely control a distant PC is CrossLoop – just install it on your machine and have someone do the same thing at the other end and you are away. Before you get your hopes up, let us say that it is no substitute for the products above that allow you to login to a remote PC without anyone in attendance. By contrast, CrossLoop requires someone at the other end. If you can live with that limitation, CrossLoop may just what you have been looking for. It works like this:
The user on the remote PC runs CrossLoop and generates a random 12 digit key which they send to you by email, phone, whatever. You plug this key into a copy of CrossLoop running on your own PC and request a connection with the remote. If the remote user accepts the connection you can then take control of the remote PC. At all times the user at the remote sees on his screen exactly what is happening.
That’s pretty much standard remote computing, but it is the ease of use that makes CrossLoop different. No complex commands or firewall configuration are needed, just the ability to follow simple on-screen instructions. It supports 128-bit Blowfish encrypted connections and allows for two-way file transfers between the client and host PCs. Unlike Windows Remote Desktop, it will run on any PC from Windows 98 onwards. Just the thing for helping a friend with a PC problem, remote support or remote user training. Version 2 adds creation of a free CrossLoop accounts to create a dynamic public profile page, reserve your custom CrossLoop URL, view your session history, as well as widgets to promote yourself as a tech support specialist.

An alternative to VNC-based products is the free version of the commercial remote access product LogMeIn. This is a web-based service that’s extremely easy to set up and use and can be accessed from any PC with a browser. The free version won’t allow file transfer or remote printing but is a great solution for accessing your remote data as well as file sharing. Registration is required.

UltraVNC Full of features including file transfer and easy to install and use. Can run as a service for unattended access. Needs ports opened through firewall to access from remote network. Not very easy to get a quick remote session going with someone across the Internet. http://www.uvnc.com/ http://www.uvnc.com/download/index.html 1.98MB    1.0.6.4    Open Source Freeware (includes program code)    Windows 2000 – Vista 64 Bit version available Since this is an active product there are updates made on a regular basis to fix security or stability issues. You should check the download page often for these updates.

LogMeIn Possibly the fastest most reliable remote control freeware available. It will even allow a PC to remotely control a Macintosh. Excellent tool for accessing home computer or friends/family computers from anywhere. Requires registration. You will have to pre-install the software on machines you wish to remote control or create a spare account that you can give the user name and password to for people that are remote. http://www.logmein.com https://secure.logmein.com/products/free/ 10.2MB    N/A    Restricted Freeware (full commercial version available)    Windows 2000 – Vista , Macintosh (Registration required)

UltraVNC SC Does not require installation and allows end-user to receive support by clicking and running a single download. Automatically removes all traces of program upon end of remote session. Allows for custom branding and extensive customization including 128 bit encryption. Requires much configuration and either a place to host the repeater or open ports in firewall of the supporter. http://www.uvnc.com/addons/singleclick.html http://www.uvnc.com/addons/singleclick.html 166KB    N/A    Unrestricted Freeware    Windows 2000 – Vista There are detailed instructions available on the homepage of how to configure and customize the application interface.

Crossloop Easy to install and has many features including File Transfer. Uses the Crossloop servers as a connection point so all that is required is an outgoing connection which means that no firewall ports have to be opened for incoming connections. Requires the person on the other end to download, install and then tell you the host access key before the session can begin. http://www.crossloop.com/ http://www.crossloop.com/ipage.htm?id=predownload 2.45MB    2.44    Unrestricted Freeware    Windows 2000 – Vista , Macintosh There are good helpful instructions on troubleshooting problems and getting the most out of Crossloop at http://www.crossloop.com/help/help_home.