To work on the controls requires only a browser and text editor.
I'm actively developing Commander, so if you check back in a couple days it will probably have an XY control. No guarantees...
Your bigger task is building out the robot side and getting the software to drive it hooked up and under control of the Bitlash interpreter on Arduino. Once you can control your robot from the command line, it's ready for a Commander control panel.
The tricky part about implementing "go forward" and "go left" at the same time is not at the control panel end, it's on the Arduino where you have to work out how to walk and chew gum at the same time. To go forward 10 and left 5, for example, you can just go forward 10 and then go left 5, but most people probably expect that a robot will go forward a little and left a little to more or less move in a straight line. So you end up breaking larger moves into smaller ones you can interlace. That requires a little thought.
-br