It's a software implementation of 'Confederate Army Cipher Disk' programmed using 'C'. To know more about this cipher disk visit: https://www.youtube.com/watch?v=y94Mfvr2pKI
The inner ring of this disk implementation has alphabets in reverse order as in: https://www.britannica.com/topic/cipher-disk
To compile and execute it online, visit: http://www.tutorialspoint.com/compile_c_online.php