Open source does not mean free applications.

If Yongzh is using open source code, then he should credit the original authors, and provide his modified source to comply with the license. At the same time he should be free to sell the compiled APK at whatever price the market is willing to pay for it. You are then free to compile and modify the code as desired.

Yongzh's emulators are the best I have used on Android, and am glad to support him with purchases. I would hate to see him go because of some uppity trolls. I'm actually disappointed to see this app listed for free now, got a feeling that motivation will drop significantly, and quality will as well.