Kimai is a web-based multi-user time-tracking application
Free admin dashboard template based on Bootstrap 4
Stripe.net is a sync/async .NET 4.6.1+ client
Laravel Cashier provides an expressive, fluent interface to Stripe
A library that can help you with generating PDF documents
Telegram Bot API for NodeJS
Free Bootstrap 4 admin/dashboard template
Fullstack open source Invoicing application made with MongoDB
Library offering classes to read from and write to spreadsheet formats
Sistema de Facturación Simple con PHP, MySQL y Bootstrap
JavaPOS implementation and more, for Brazilian Retail applications
Shipping biller is benificial tool for generating shipping bills.