vine viewer & server for macs

Vine Viewer and Server a mac-only viewer and server for vnc-based desktop sharing. Server is free, viewer costs $30.

Chicken of the VNC - mac-only viewer

Chicken of the VNC a free opensource mac-only viewer for VNC protocol of desktop sharing. Hosted at sourceforge.

ScreenRecycler - mac-only viewer

ScreenRecycler is a commercial closed-source mac-only viewer (for $25) for both mac intel and mac ppc.

It claims to be the best client for desktop sharing on mac. Seems not to support http server like many vnc servers can do.

teamviewer - commercial windows-only closed-source

TeamViewer commercial windows-only expensive closed-source product based on VNC. Created by German people. Costs $218 (!) per copy of most cheap edition. There is a free edition (it's unclear whether free edition is only viewer, or it's viewer + server).

It seems not to use any drivers for screen capturing (since it does not require admin rights for installation) so it should work much slower than tightvnc and ultravnc.

UltraVNC - free windows-only VNC implementation

UltraVNC is a windows-only free open source implementation. It's hosted on sourceforge too.

TightVNC

TightVNC - most advanced free version with source code. Forked by Russians (or Ukrainians) to implement better protocol compression, it's in top 10 most active projects at sourceforge.com. No Mac version of the viewer. Recently they've started TightProjector commercial product for broadcasting screen session on Windows.

realvnc - the creators of VNC protocol

RealVNC the original authors of VNC protocol have formed this company.
Cost is $30 for personal edition, $50 for Enterprise Edition.