I do JSON edits for the game Cataclysm: Dark Days Ahead to achieve the following:

• Balance weight
• Get items into itemgroups
• Update mapgen
• Do some tileset work including adding json for sprites and adding looks_like to other entries
• Creating new content like the small railroad track

I also have my own repository that contains a couple of tools to help analyze cataclysm's json to enable me to do the above tasks.