I have got a mostly working VNC (virtual network computing)
viewer for GNOME. It currently supports enough of the VNC protocol
to be useful (all pixel encodings except hextile).
The authentication code in the package is a modified version of
the DES code in samba (ie. it is not a full implementation, and is
only useful for hashing passwords for authentication), so make up
your own mind about whether it is legal in your country.
It currently doesn't support clipboard transfers and hextile
encoding, but does allow you to set the display to a bit depth not
matching your visual and make it display correctly (eg displaying
16bit from a 16bit connection to a 24bit visual), so you can reduce
the bandwidth usage of the viewer without going all the way down to