I use Plain TeX for typesetting, and it is good. (I don't use LaTeX. I think Plain TeX is better. And, for making fonts, METAFONT is better.) But to render TeX

I use Plain TeX for typesetting, and it is good. (I don't use LaTeX. I think Plain TeX is better. And, for making fonts, METAFONT is better.) But to render TeX documents you will need to implement TeX. (You could, however, implement a TeX macro package that you can then use the same input for multiple kind of output.)