This is v2.1 of a Basic Interpreter by Phil J. A. Cockcroft
earlier versions used to be known as Rabbit Basic.

According to an earlier licensing document:

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This code is being put in the Public Domain since I will soon loose
network connectivity (I am leaving my job) and I don't particularly want
to sell it. This system does not contain any proprietary software. All
the algorithms are original or come from publicly available sources.

There are no licensing restrictions on this code or documentation at
all. I only ask that you give appropriate credit to the author.
===

So, there you have it. :)