Google Docs supports multiple simultaneous editors and tracks revision histories. It was a lifesaver for group projects in college.

And while 'always online' is often a bad thing, it seems to be a lot more reliable than the alternatives of email chains with the attached Word document, appending -R3-edited-complete-final-done.docx to the filename, the manual merges when two people are working on the same thing, or the USB stick that gets passed around.

Word change tracking is for word users like democracy. It's a bad system, but all alternatives are worse.

LaTeX + git

It would be interesting if someone could write a program that could diff two LaTeX documents and produce a change-tracked version showing insertions and deletions.

I think it's doable, but it's a serious project.

It's done and it works very well (in my experience) for comparing two revisions of a document: https://www.ctan.org/pkg/latexdiff

Plain old diff does just that.

I'm assuming that what you're actually asking for is a pretty GUI that pretty-prints diff's output.

latexdiff does exactly that: https://www.sharelatex.com/blog/2013/02/16/using-latexdiff-f...

Being a text format means that you can use version control effectively. Latexdiff can generate diffs between versions. Wouldn't call it better, just different.

Sharelatex if you want something that's easy to get started with for non-programmers (As opposed to Git)