Payments
Record a payment in seconds. Pick the customer, pick the invoice from their open ones, and the amount fills itself in. ContaCash refuses to pay the same invoice twice, and the journal entry is written the moment you save.
The other direction works the same. From the outstanding creditors report, click a supplier and see every open bill with its remaining balance, with the pay link right there, the form pre-filled.
Bank accounts and transfers keep the money side tidy, and reimbursements cover what you paid out of your own pocket on the company’s behalf.