Invoice Ninja - Invoice Ninja is a free, open-source solution for invoicing and billing customers.
Toggl - Toggl is an online time tracking tool. It features 1-click time tracking and helps you see where your time goes. Free and paid versions are available.
InvoicePlane - Free and open source invoicing application to host on your own server.
Harvest - Simple time tracking, fast online invoicing, and powerful reporting software. Simplify employee timesheets and billing. Get started for free.
Billdogg - Beautifully simple invoicing for freelancers
TimeCamp - Simple and robust time tracking app to help you stay on the same page with your team while working from home.