Online version of 500.
Get Python, 3.4 or later.
Run the following comands in terminal:
pip install bottle
python server.py
Then have fun.
If you wish to save game data between runs of the server, you can use the -f command line argument to save the data to a json file. The file may not be compatible between different versions of the program. This argument is usefull if your server occasionally crashes in the middle of a game, or if you know you will have to suspend a game.
Bottle relies on an underlying web server (which, by default, it supplies itself). You can change this with the -s command line argument. For example, python server.py -spaste will run the server and use paste as the underlying server.
This requires you to install the respective server with pip.
You can select which port the server connects to from the command line with the -p command. For example, to run on port 80, you can use python server.py -p80.
Use Git or something.