What is the crowd's opinion of NXT Field Control Free?

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One option if you're just running demos:

There's an android app that connects to the NXT over bluetooth and lets you run standard NXT FTC RobotC code. You can then build a robot with the NXT, old hitechnic controllers, etc., without a Samantha or a Field Control system, gamepads, etc. You hold the android device like a gamepad and it has buttons on the screen that emulate the normal gamepad buttons.

The app is available here (free version) or here (paid version with a few other features like being able to plug a gamepad into the android device and use it instead of the buttons on the screen). I am not affiliated with these apps at all but we used to use them for demos and they generally worked well.