GIT

Version control is very important in software development, and one of the most popular version control software is GIT, however it can also be used for other things where you need to have text based files changing over time in a safe manner, and collaboration. From writing documentation using LaTEX or Markdown, to writing music using LilyPond, or mechanical designs using OpenSCAD, and many other things.

GIT allows you to, change files and comment on the reason for those changes, have several people working on a file or set of files independently, and then safely merge the changes, annotate any snapshot of the project for release or easy reference, look at the change history, with several degrees of detail, and many other things.