I am only aware of three on-demand ERP systems – Intacct, NetSuite and
Aplicor. Intacct was developed on a PHP/Oracle technology stack and
its customization tools are largely limited to simple configuration
and integration. NetSuite is a Java/Oracle foundation and the company
offers a proprietary development platform called SuiteFlex which
permits customization and development of third party applications.
NetSuite also offers SuiteScript, a javascript derivative, to
customize pages and modify built-in workflows. Aplicor was developed
in .NET (C#) on the SQL Server database and the company offers an API
and web services (with WSDL) library which permits integration or
customization using Visual Studio.net.