Have you read the site? Realm Crafter proudly announces that its scripting language is "loosely based on BASIC, with C influences". Blitz3D is based around BASIC. BlitzPlus uses a BASIC/C hybrid.
Seriously, how many warning signs do you need? I'm all for fan development, but this engine looks like it'll turn away developers (non-free and single-platform) and provide a horrible working environment.
Contrary to belief, I only naysay when there is something valid to naysay about. Unfortunately, that's nearly all the time.
Also, since I noted it came up various times, note that while it has not been tested in court (in other words, don't stick your neck out
), copyright law suggests that game mechanics cannot be copyrighted.
~J