Not a feature list - the jobs. Each one is a thing somebody sat down to do, with the invoices they already had.
The month's folder in, one checked table out, with the two files that would not read named instead of skipped.
The same invoice sent twice under two file names, caught by supplier and invoice number - before it becomes two payments.
Every original kept as it came in and addressed by its content, so March's invoice can be produced when somebody asks for it.
No upload, no account, no network - and an archive that is a folder on your own disk.
Everything happens on this computer - your invoices are never uploaded.