https://share.allegorithmic.com/libraries/2884Saves current file and makes a numbered back-up copy (filename_autosave_1/2/3.spp) in the same folder. Cycles through several numbered backups.
Autosave delay and number of backups can be configured via Plugins -> autosave_tl -> configure.
Windows-only restriction is due to dependency on a small file copying utility I wrote for this plugin. If Painter's plugin API ever gets a file copy method (right now it only has read/write methods), the plugin can be easily made platform-independent. As an alternative, someone with access to Mac/Linux dev tools could port the autosave_manager utility for these platforms.
Tell me if there are any issues.