Piggy-back method for simultaneous access by 2 users
Here's a "piggy-back" method for simultaneous access to one computer ("Target") by User 1 and User 2, if User 1 trusts User 2.
User 1 creates a LogMeIn account. User 1 then installs LogMeIn on his computer. This means User 1's computer shows up as one of "my" computers when User 1 logs into the LogMeIn web site. User 1 then installs LogMeIn on the Target computer. This means the Target computer shows up as another of "my" computers when User 1 logs into the LogMeIn web site.
Next, LogMeIn needs to be running on User 1's computer and on the Target computer.
User 1 goes to the LogMeIn web site, logs in, and connects to Target. Target's desktop now shows on User 1's computer screen.
Next, User 1 gets on the phone and gives User 2 his log-in credentials. User 2 goes to the LogMeIn web site and logs in as if he were User 1. In effect, User 1 has two sessions running through the LogMeIn web site.
After logging to the LogMeIn web site, User 2 gets the standard "my computers" list, which has the User 1 computer and the Target computer.
Now for the Evil part: User 2 clicks on the green button to connect to User 1's computer!
The result: User 2 sees User 1's desktop, which is seeing Target's desktop. (Hence the term "piggy-back," which I've just made up.)
User 2 can move the mouse on Target's desktop, because it's as if he's sitting at User 1's computer, which is already connected to Target. User 1 can move the mouse on Target's desktop because, well, he's already connected to Target.
Kewl, yes?