When I studied I have done – as some thesis – radiotelex simulator. I think it still can be useful to somebody, so I decided to release it under GPL.
The program simulates operation of radiotelex. If you are conneted to TCP network, you can really communicate between instances. It also simulates automatic shore stations, so you can connect to them, check weather forecasts, receive messages etc. It is educational tool – if you don't know how to use radiotelex and have nobody who could explain you, and you can't read Polish documentation of this program, probably it won't be funny for you.
Simulator's user interface is in English. Documentation is in Polish, but if you plan to use the program and have some problems, feel free to contact me.
The program is a free software released under GPL.