ChromiVNC is an implementation of a VNC Server which runs on Macintosh. 
It works well with the VNCThing VNC Viewer.

You can get it here: http://www.chromatix.uklinux.net/vnc/index.html

If you'd like the Drag Manager to work with this flavor of VNC, 
be sure to install vncpatches68k:

http://amcg.th.ic.ac.uk/~adrian/vnc/

These patches are needed by ChromicVNC on both 68k and PPC if 
you want the Drag  Manager to work.

Thanks to Lex Ein for the info!