free multi-user remote desktop utility

Is there a free remote desktop utility that allows multiple simultaneous 
user logins? I've been using Windows RDP as well as TightVNC so far, and 
they are both fine. But what I'd really like is something that will 
allow users to remain actively logged in without suspending them in the 
background when somebody else logs in. I believe Windows Terminal 
Services and Citrix does this, but of course neither of them are free.

	Yousuf Khan