Caetla was a GameShark firmware replacement for the Playstation. It was created specifically for the original GameShark with the white cart and is not compatible with the GameShark Pro. It was originally produced by kcomm for use as a development tool, and was then leaked onto the Internet.
Most versions of Caetla could be used to run out of region and pirated discs on an unmodified Playstation. Later versions had a massive flaw in that they stored codes on a special memory card file. The problem with this is that the program to create the file seems not to exist.
Homebrew PSX cheat device ROM for flashing to old PC Comms link devices. v1.28b is a hacked version.