Is there a good accounting app for personal trainers?

I use Ring It Up Pro, can customise your invoice, run statements for those clients who pay monthly, intergrates with PayPal button on invoices for those ad hoc clients to pay. Invoices and receipts of payment are emailed direct from your phone which eliminates the printing and mailing out; keeps operating costs down. Keeps track not only of invoicing but also expenses. It’s the best that I’ve found and the easiest to use.