Per-client timeline of every sale, invoice, payment, return, and credit. The foundation of "treat customers like individuals, not transactions".
Clients → pick a client. The History tab shows the full chronological list.
By date range, by document type (invoices, payments, returns), or by amount range.
Click any row to open the original sale/invoice. From there you can re-print, email, void, or process a return.
Sidebar shows aggregates: lifetime value, average order value, frequency, last purchase date, preferred products.