vncssld is a VNC SSL repeater for Unix. You can use it to access your user's desktop using VNC SSL. The advantage of using a repeater is that you don't need to configure your firewall to be able to connect to your user's desktop: both VNC server and VNC client connect to the repeater. Since it is using SSL, It can even work using a standard HTTP/HTTPS proxy (like squid or DansGuardian).
Guacamole is an HTML5 Web application that provides access to desktop environments using remote desktop protocols such as VNC or RDP. A centralized server acts as a tunnel and proxy, allowing access to multiple desktops through a Web browser. No plugins are needed. The client requires nothing more than a Web browser supporting HTML5 and AJAX.