I got tired of messing up missions and not being able to revert to a good point, so I made a simple plugin to version control the saves directory using Git. Jebretary is probably a better choice for most people, but if you know your way around Git and just want a simple plugin that does commits, then maybe KerbalGit can be of use.
The plugin is very basic and doesn't have a UI. Don't install KerbalGit unless you are comfortable using Git!
When first run, the plugin will set up a Git repository for the saves/ directory. The .git/ directory itself is placed in GameData/KerbalGit/. The plugin is invoked and commits changes on three events:
save in VAB/SPH
I have only tried KerbalGit on Windows. The plugin uses LibGit2Sharp 0.17 which relies on the the native library libgit2. A Windows binary (git2-06d772d.dll) is included, but separate builds are needed for Linux and OSX.
Get the latest release.
Copy GameData/KerbalGit/ to your KSP directory.
Copy git2-06d772d.dll (on Windows) to the root of your KSP directory. Pick the correct one from NativeBinaries/ depending on if you run KSP in 32-bit or 64-bit mode.
You can exclude any files and directories that you don't want to have under version control in saves/.gitignore. In GameData/KerbalGit/settings.cfg, you can set the minimum interval (in seconds) between commits and the committer's name and email.