[dbmueller]

I'm pretty sure the first two links refer to something very different than the third:

The first two are about a way to encode maths using unicode, as in conventions and special characters allowing e.g. to write fractions, aligned equations, etc. So, this would essentially furnish an alternative to the "math" subset of latex (think mathjax or katex) or mathml.

The third is a package for latex, and allows to use unicode symbols (greek letters, math symbols, etc.) in your math environments + something related to the use of unicode in the output (requiring compatible fonts); it seems the second part is the main one but I'm not sure what that means exactly.

[mkl]

The Latex package says "Maths input can also be simplified with Unicode since literal glyphs may be entered instead of control sequences in your document source." So it at least includes a similar idea.

[dbmueller]

Superficially similar, yes, but my point was just that it may seem from your bunching up the links together that all refer to the same thing, while they don't.