Because I'm involved in many collaborative projects, some of which luckily involving LaTeX, and because I'm trying (sort-of succeeding) to spend as much time as possible outside the office (mostly failing) to work on the books, in the past few weeks I've found myself wanting some track-changes utility for the work I was sharing with my LaTeX-savvy colleagues. [Could this be a candidate for the longest opening sentence of a post, ever?]
I had a quick look online and found this very nice package $-$ it's probably well established, but I'd not encountered it before, so I was very pleased to discover it.
It works quite smoothly and lets you annotate the original .tex file with changes, additions and notes. And what's even nicer is that the compiled document has some mark-up (eg different colour for new text), but it's not very cluttered, so that you can read fairly easily the current version with notes.
Speaking of LaTeX, I also found this other couple of useful programmes: the first one is a perl script that creates the bibtex code of a given reference $-$ basically you can copy and paste the full reference of a text of interest and the script will return the LaTeX code to paste into a .bib file. The second one searches PubMed and retrieve the LaTeX code for the hits that match the search string.
Again, both are probably quite old and well established. But it was quite serendipitous.