GnuCash - A personal and small-business financial-accounting software, licensed under GNU/GPL and available for Linux, Windows, Mac OS X, BSD, and Solaris.
TaxJar - TaxJar simplifies sales tax filing for eCommerce sellers.
Synder - AR Automation
Thomson Reuters ONESOURCE - ONESOURCE tax software and solutions synchronize every aspect of your work and link international, country, state and local tax laws.
Xero - Xero is online accounting for your small business.
Vertex Cloud - Vertex Cloud offers sales and use tax automation solutions.