Jenkins - Jenkins is an open-source continuous integration server with 300+ plugins to support all kinds of software development
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.
CircleCI - CircleCI gives web developers powerful Continuous Integration and Deployment with easy setup and maintenance.
ChargeOver - ChargeOver automates recurring billing, subscription billing, & payment acceptance. A SaaS that integrates with Xero, Quickbooks, & has an API. Free trial.
Travis CI - Focus on writing code. Let Travis CI take care of running your tests and deploying your apps.
Elorus - A super-easy online invoicing & time tracking software