A guy who plays in the spring lobby wrote a Java client a while ago since tasclient doesn’t run under Linux/mac natively. He didn’t tell many people and before he could implement the battle protocol, the project was cut, and he went off to university. The client may not be the best thing since sliced bread but it’s a nice example, and has a few hidden gems in its source code.
Orakio has given permission to do as we please with his source, and has put it forward with no licence whatsoever. So here is a compiled jar program and the source code.
He’s currently working on an open source C++ server and a client in his spare time.