Equivalent to Double Vision

[Michael Scully]

In my Unix days, I used a support tool called Double Vision that allowed
someone to take over another tty session.  This was immensely useful, so
that you could debug their actual session, not just try and create the
problem from scratch.  Our application is character based, and the users
have telnet or ssh sessions going that launch the software.  I am guessing
that this product did something like a Tee command to repeat all the same
screen I/O to multiple tty devices.

I know the company who makes this product is still around, and has a Linux
version.  But I was curious is something like this already existed as a open
source equivalent.

Scully