This applet runs a slightly modified version of Cigol for demonstration purposes. Download the full version for full functionality (and source code).
If you get the "This Cigol context is invalid" message, it's actually ok to continue using Cigol. The command line version of Cigol does not persist to print this error, but embedded versions (such as the one used by this applet) do.
The reset-applet: directive will reset the state of the
knowledge base.
The readme file has complete instructions for the full version as well as a tutorial that can be used with this applet.