Fanurio is a time tracking and billing application designed to help freelancers manage their work and be paid for it. You can organize your work per client using projects, mark invoices as paid and track the overdue ones, mark your work as billable (flat rate, hourly rate) or non-billable, create partial invoices at any time during the project, create invoices for single or multiple projects, customize invoice templates using your own layouts, import clients from other applications by means of a CSV file, export data to a CSV or Excel file, and create backup copies of your data.
Invoice is a simple application, written in Obj-C/Cocoa, to manage your articles, tasks, projects and invoices. You can create invoices from tasks, articles and just manually entered lines. Add a PDF file as background to your invoice template. Then add autofields like date,invoice number, company name etc. to your template.
iRatchet is a Tiger-only Invoicing and Billing application written in Objective-C/Cocoa. iRatchet provides the features and functionality common to billing and invoicing apps, (tracking hourly and fixed entries, multiple clients/projects, timers, pdf output, emailing of invoices, etc.),
iSous is an invoice manager program. With it you can merge invoices using Pages. You can also track those invoices and record payments.
(shareware) TimeNet is an invoicing, billing, and time management solution.