I AM NOT RESPONSIBLE FOR ANYTHING YOU OR AN EXTENSION DOES TO YOUR COMPUTER!
A CLF Extension is an executable file written to add functionality to the program. Extensions can be made to do anything, and may be written in any programming language. An Extension has to be a useful console application to be accepted and added to the extension list.
CLF Extensions are .exe files. They are installed by adding the exe file to the extensions folder, and creating an alias to execute the extension. The exinst command does this automatically. To install an extension with the exinst command, the extension must be accepted and added to the extension list.
Here are instructions for creating extensions.