Check Gobby if you want to edit/share documents with someone.
Wow! What a wonderfull article here
http://www.yuuguu.com/home its free, it has win/mac/linux versions!
http://www.nchsoftware.com/screen/index.html
A free software that lets others watch your screen in real time. No need to install any software, which is a plus. Works with Windows, Mac and Linux.
CroosLoop is also very easy to use, but requires that each party install the CrossLoop software onto their computers. Uses 128-bit encryption and allows for file-sharing also.
https://secure.logmein.com/home.asp?lang=en
Another popular service for remote desktop sharing. Easily access remote PC’s by installing a client software onto each machine. Good for remote PC trouble-shooting, etc.
A good free tool for online collaboration, desktop sharing, and remote PC access. No registration required, no logins, very easy to use. Uses SSH to make connections to other PC’s.
SkyFex allows remote watching and remote control in real time. Does not require additional software installation and works transparently through NAT and Firewalls. Only for IE though.
http://www.teamviewer.com/index.aspx
TeamViewer has a couple of features, such as remote control of PCs, screen sharing, file transfer, chat ability, and is secure. Optional install for the TeamViewer software for it to work. NonComersial version available for free.
Free client and server software for Linux
FreeNX: Homepage
FreeNX: Download
Not free but the original and the best