There is one that comes with XTools Pro (paid).
https://xtools.pro/en/features/general-usage-tools/auto-save-mxd/
I can see a few posts in ArcGIS Ideas like https://community.esri.com/ideas/1079
In ArcGIS Pro, you can autosave edits.
http://pro.arcgis.com/en/pro-app/help/editing/customize-how-you-save-edits.htm
