Not sure if they appreciate me sharing a link, but apkmirror.com is what I believe to be a reliable storage and has a great search function.

I run ACDSee on pc to manage photos that are stored on or are synced to my diskstation. However I hardly fire up my laptop anymore and do most using f-stop.

I have an older diskstation, but I believe new DSM supports Syncthing that can replace DS Sync well.