To be on the safe side, you should not provide KiXtart with your commercial product but link to KiXtart.org where your customers can download the KiXtart package.

Alternatively, you can try to contact Ruud van Velsen (the developer) or contact Scriptlogic/Ruud through http://www.scriptlogic.com/kixtart/default.asp , there's an email address on the right side that you can use (KiXtart2001@hotmail.com).

However, you are definitely not allowed to commercialize KiXtart itself, thus you're not allowed to sell KiXtart.
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There are two types of vessels, submarines and targets.