Sure this is a free game on Linux, but the Mac version has not been updated on the developer website for a long time, and cannot just be downloaded and installed like on Linux. Rather than screw with getting it installed via Macports or some emulator, for 99¢ I just paid up and can now easily play on MacOS or iOS, although it is difficult on a phone due to lack of precision controls (no shift key). If I could recommend something to the dev for the phone version, add a precision control button on the right like how there is a swing button on the left. That would make the iOS version more usable.