No. Installation of client software is not required to access SSL-Explorer. This is one of the core advantages of SSL VPNs over existing VPN technologies. SSL VPN solutions are often referred to as 'clientless VPNs'. Whilst not strictly true (a client is still required for some features), the client is dynamically loaded over the internet using the Java applet technology and therefore does not require software installation as with native VPN clients.
A number of features within SSL-Explorer require the use of the VPN Client, a Java applet that is embedded in the web browser when launched. In order for the successful running of the VPN Client it will be necessary to have a JVM installed on your machine. Thankfully, most modern browsers support Java by default and this is usually not a problem.
SSL-Explorer supports all Sun Java Runtime Environments (JRE) and Sun Java Development Kits (JDK), as well as the Microsoft JVM.