This project is unmaintained, but feel free to fork it.
This plugin serializes GameObjects using JSON. It has a range of supported types built in, but more can be added manually. I am developing this in tandem with my Deus Ex-based game project The Vongott Chronicles
It can be used for savegame files, custom level editors, carrying over information between scenes, and it probably has more applications than I can think of. If for any reason you'd want to manage your resources externally, this is your plugin.
In the wiki
MIT