What analog of windows remote desktop for FreeBSD supports s
NX is, especially across slower network links.
VNC can be as "fast" as RDP, if you use the right command-line options. For example, the default options make remote access to a 1024x768 screen over an E10 connection unpleasant to use. But:
$ vncviewer -encodings "tight" -depth 16 -compresslevel 9 -quality 5
is very useful over 1.5 Mbps ADSL links, even to computers with multiple monitors.
We use VNC as part of our helpdesk setup, connecting to remote screens all around the district. Some sites have < 2 Mbps wireless Internet connections, some 1.5 Mbps ADSL, some 10 Mbps E10, some 100 Mbps E100, some gigabit fibre. Using the options above, we have no issues with VNC "speed".
And we even tunnel it over SSH.
The downside to VNC is that it's a remote/shared console protocol, showing whatever is on the screen. It's not a remote login protocol like RDP/Terminal Services/XDMCP/NX.