As i no longer play Minecraft, and haven't done for a couple of years, i no longer have any interested on maintaining this. Releases of something like a successor can be found here: https://github.com/zlepper/go-modpack-packer/releases, however that project is not maintained either.
Technic Solder Helper is a tool that helps you pack modpack files in the correct format.
Supports Technic and FTB packs. AT Launcher are in the works.
A compiled version of this can be found at: http://zlepper.dk/solderhelper/publish.htm
For linux run the command
curl https://raw.githubusercontent.com/zlepper/TechnicSolderHelper/master/TechnicSolderHelper/install.sh | bash, this will install the program in a subfolder of the current working directory, though it can be changed in the script.
For Mac I have no idea if this will work or not. I don't have a mac, so I can't test.
If you want to contribute to TechnicSolderHelper you need the following things on your machine:
If you are using Windows to develop i would recommend getting visualstudio: https://www.visualstudio.com/
Or if you are using linux or mac monodevelop: http://www.monodevelop.com/download/ (Will also work for Windows)
Then download the code using your prefered git tool and open the TechnicSolderHelper.sln file with the IDE you just installed. Then tell you IDE to restore packages and you should be good to go.