Haven’t tried this but promising (though not free). It involves hosting your own server, troubled user simply click on a link in an email or visit your support website. According to screen connect website’s demo, no software install is required on client side.

Would like to find similarly elegant but free solution though.

I came across two programs that I’ve found very helpful – one is free and the other isn’t. So first, one should differentiate between screen sharing software, which allows you to see what is on another person’s computer, and remote control software, which allows you to actually control that computer from a distance.

For screen sharing (for meeting purposes) I tried DimDim and it’s great. I used to use GoToMyPC for $50 per month but this works just as well and it’s FREE. They also have a “Pro” version with more features for $20 per month.

For remote control (for troubleshooting, accessing your files, etc.) the best that I’ve come across is Proxy Pro 6 from Proxy Networks. It’s the most secure such program out there and the features are great. Full disclosure – it’s not free and you do have to install it. It’s well worth it though.

Yesterday, I came cross DESKTRA freedom desktop on download.com.

I have installed and tested the software. It’s free, simple to use, really fast and the remote Desktop screen color looks just fantastic. You don’t have to worry about the firewall settings, etc.

Give it a try and let me know what you think.

http://www.desktra.com/freedom

Cheers,
Lutz

ShowMyPC is the best, no installation required, I can vouch for it.
Hope this helps.

A few months ago I did a very brief experiment with a colleague using LiveLOOK (http://www.livelook.net), a screen sharing app with no downloads. I seem to remember it worked well for the very brief test, but I haven’t revisited it since.