http://guacamole.sourceforge.net/
What is Guacamole?
Guacamole 0.1.5, served by an Amazon EC2 instance.
Guacamole is an HTML5 + JavaScript (AJAX) viewer for VNC, which makes use of a server-side VNC-to-XML proxy written in Java. The current version is almost as responsive as native VNC and should work in any browser supporting the HTML5 canvas tag.
Guacamole provides access to your VNC server through a VNC-to-XML proxy written in Java. The server-side half of Guacamole thus requres a servlet container like Apache Tomcat, while the client-side requires nothing more than a web browser supporting HTML5 and AJAX.
The main project page is here: http://sourceforge.net/projects/guacamole.