minecraft-pi may be provided free of charge, but it's not in any way free or open source. Here's the minimal licence provided with the distribution (in
*** The real license isn't finished yet, here's what goes in plain english ***
You may execute the minecraft-pi binary on a Raspberry Pi or an emulator
You may use any of the source code included in the distribution for any purpose (except evil)
You may not redistribute any modified binary parts of the distribution
minecraft-pi was written by Mojang, so it uses the company's intellectual property.