From Delbert Hall:
LoanMeister uses the power of Microsoft Excel to make it quick and easy to produce an amortization table for a loan by simply entering the amount of the loan, the interest rate, the term of the loan (in months), and the starting date of payments. LoanMeister allows you to track payments by entering the amount paid each month, along with the date of the payment and the check number. LoanMeister also has the ability to automatically update this table when the borrower makes payments in excess of the minimum monthly payment. This Extra is applied directly to the principal of the loan, thereby reducing the balance, and potentially the total number of payments required to pay off the loan. Works on both PCs and Macs.