[sn6uv]

There's also Mathics (I'm one of the maintainers).

> but with such a huge size, the language would be near impossible for one single individual to implement a compatible version.

As a single individual who has tried, yes it's impossible but a subset is doable.

[gertef]

The inventor of Mathics got a job at Wolfram :(

http://www.poeschko.com/