GnuCash - A personal and small-business financial-accounting software, licensed under GNU/GPL and available for Linux, Windows, Mac OS X, BSD, and Solaris.
vatlayer API - Free VAT Validation & EU VAT Rates API
Synder - AR Automation
VatStack - Simplify VAT & GST for your digital business.
Xero - Xero is online accounting for your small business.
TeamLogger - Simple, employee time-tracking software with automatic screenshots and activity level monitoring. $1 / User / Month.