Zoho Invoice - 100% free online invoicing software for small businesses.
Joist - Joist is a mobile application to manage estimates, invoicing and accounting for contractors.
FreshBooks - The ideal accounting software for small business owners.
Estimates App - Quick Estimation & Invoicing App. iOS, Android, Windows & Online @ https://estimatesapp.com/
Invoice Ninja - Invoice Ninja is a free, open-source solution for invoicing and billing customers.
Avaza - Beautiful Projects, Timesheets, Expenses, Quotes & Invoices for Small Businesses