Invoice Neko is a self-hosted open sourced invoicing system built on a modern backend with a focus on delivering a good user experience throughout the application
Manta is a flexible invoicing desktop app that allows you to quickly make beautiful invoices without the need of using design software like Photoshop, InDesign or Sketch. It's geared toward people who need to make invoices from time to time such as freelance designers, developers, photographers or writers ... etc. No Internet, monthly fee required!
This free overdue payments reminders generator helps to generate quick emails reminding your clients about overdue payments. 100+ unique variations. Integrates with GMail. No signup required.