The filesystem manager is the core subsystem in charge of reading and writing “user” data. This is intended to serve as the way of creating and accessing save files, and any other data that can be conserved between sessions.
Data are stored in a folder in the users's native “home” directory on the system. On Linux, this folder is hidden (/home/<login name>/.<app name>). On windows, this is a folder on the user's directory (C:\Users\<login name>\<app name>)
Save files are stored as simple plain text “key = value” files.
Reading and writing data on disk is a slow operation. Save files are cached in ram, and have to be explicitly written to disk to be actually saved.