Joist - Joist is a mobile application to manage estimates, invoicing and accounting for contractors.
BillGrid.com - BillGrid is an easy to use online invoicing, billing and expense management system that will save you time with tracking clients projects, expenses, invoices and payments.
Estimates App - Quick Estimation & Invoicing App. iOS, Android, Windows & Online @ https://estimatesapp.com/
ChargeOver - ChargeOver automates recurring billing, subscription billing, & payment acceptance. A SaaS that integrates with Xero, Quickbooks, & has an API. Free trial.
Invoice Ninja - Invoice Ninja is a free, open-source solution for invoicing and billing customers.
fusebill - Fusebill is the leading recurring billing and subscription management software for businesses. Try Fusebill for subscription billing made easy!