This is a pretty basic Minecraft Modpack "manager" that I cobbled together in a few hours. It takes in a Flame-like manifest.json and produces a zip file containing a filled-in manifest.json and the overrides folder specified in the input file. The input doesn't require fileID filled in and also has some custom variables.
modpkgver: overrides the Minecraft mod version to search for. (string)
modpkgIsForge: needed for mods that don't have Forge specified in their version. (boolean)