For setting campaign progress. Should work with all Freespace 2 and FS2_Open .csg/.cs2 files (it will complain if it finds anything fishy).
To use:
1) Extract the zip someplace.
2) Copy the .csg/.cs2 file you want to edit to the same folder as the program.
Windows:
3) Create a batch file by making a new text document and saving it with the extension ".bat"
4) In the file, enter "setmission (campaign file name) (mission number you want to skip to)", replacing the ()s with the appropriate values
Linux:
3) Open up a console and cd to the directory where you extracted the zip.
4) Type "setmission-lin (campaign file name) (mission number you want to skip to)", replacing the ()s with the appropriate values.
OS X:
You're out of luck, because this program won't work due to the odd architecture.

Someone wants to fix it, be my guest; all the source is in the CPP file.
Download link:
link to the attachment.